PONS schlägt vor: butty (filled roll)

http://de.pons.eu/dict/search/results/?q=bele...

I never heard of butty and don't think it's a well-known term in either the US or Canada. What's wrong with the term sandwich? A sandwich is made not only with sliced bread but also with hard or soft rolls or buns of various shapes and sizes.

*The word "butty" is often used in Northern areas of the United Kingdom as a synonym for "sandwich", particularly in the name of certain kinds of sandwiches such as a chip butty, bacon butty, or sausage butty.*

http://en.wikipedia.org/wiki/Butty_%28sandwich%29

The word "butty" is often used in Northern areas of the United Kingdom as a synonym for "sandwich", particularly in the name of certain kinds of sandwiches such as a chip butty, bacon butty, or sausage butty.

MiMo, das ist wirklich ein sehr spezielles, regional begrenzt verwendetes Wort, das ich ebenfalls nicht als Synonym für "sandwich" vorschlagen würde. Man könnte höchstens von "open-faced sandwiches" sprechen, aber auch das ist mE nicht nötig.

often used in Northern areas of the United Kingdom
Which doesn't exactly make it the obvious choice for people not from this restricted geographical area (e.g. Americans, Canadians, Brits from other parts of the UK).

What about open/open-face(d) sandwich?

Many people connect "sandwich" with two slices of bread, but an open/open-face(d) sandwich by definition is a single slice of bread with one or more food items on top of it.
http://en.wikipedia.org/wiki/Open_sandwich

While probably not a universal term, it at least has a broader distribution than "butty". (Since I am not from any of the Northern areas of the United Kingdom, I had never heard this term before, either.)

I would try and avoid the word "sandwich", as a sandwich is made with two slices of bread and something between them.
I would stick with rolls, so that your US/UK visitors don't get the wrong idea of what to expect in the bakery.

Actually, I quite like your initial attempt.

Wie's scheint, verwendet man in Chicago (pretzel) buns oder rolls, um sandwiches zuzubereiten. Da bratz mir doch einer nen Storch. – Wie heißen eigentlich Laugenweggle in Schottland? (-;

But is a "belegtes Brot" in a German Bäckerei made with a roll/bun, or with a slice of bread?

I think we are looking for a nonexistent translation when a description would be better:

"belegtes Brot" is a single slice of bread with one or more food items such as sliced meat, vegetables, cheese, or paté on top.

The OP, after all, is looking for something that will clarify for tourists what "belegtes Brot" is, not a translation of the term for a text.

Zum Vergleich / Erkennen des Unterschieds:

Belegtes Brötchen
Belegtes Brot

Auch wenn man beim belegten Brötchen den "Deckel" weglässt, bleibt es ein belegtes Brötchen.

An open-faced sandwich on a traditional/typical German hard roll called a Brötchen.

Many sandwiches actually do have only piece of bread, but for clarity, specifying open-faced sandwich is probably a good idea.

As a short (!) explanation of what to expect to find for sale in a German bakery, "open-faced sandwiches" or indeed the OP's "rolls with different toppings" is quite enough.

I was opposing the word "butty" because its use is so specific and regional that most Americans or Canadians wouldn't have a clue what it is.

Regardless of how the bread is described, "different" is a poor choice. (Actually, it's a lazy choice, which I see in much English writing and translations of German's "verschiedene" and "unterschiedliche") Depending on context, it's clearest to distinguish between "different," "differing" and "various."
In this case, I'd say "various" is the most appropriate use. When I read "different toppings", I have to ask "different than what"? I would say you could say "Sandwiches in group A have different toppings than the sandwiches in group B." In this case however, the stress is on the fact that a variety of toppings are offered and not that they differ from something (except among themselves.)
I'm sure some people will pounce on me, saying that everyone will understand it, etc., etc., etc. That may be true, but there is a fine distinction between "different," "differing" and "various." They are all common, well-understood words. There's not reason to use "different" in a one-size-fits-all fashion, especially for native speakers who should be able to "feel" the difference.

my attempt:

open-faced rolls with a variety of coldcuts, cheeses and toppings

I would have no problem using or understanding:
sandwich with a bun

@Mimo: I am very much from the North of England (currently living in Southerly regions) and while 'butty' or 'sarnie' are terms used now and again by children or as a bit of a joke term, 'sandwich' remains the regular word and involves 2 pieces of bread with a filling in between - not a roll of any kind. 'Open sandwich' best describes a 'belegtes Brötchen' IMO. One slice of bread with cheese, sausage or whatever on top.

Zu #15:

1. Die Verantwortung für die Wahl von "butty" trägt das Online-Wörterbuch PONS, nicht ich; PONS hat übrigens auch noch "filled roll" vorgeschlagen.

2. "sandwich" ist auf Deutsch ein "beleges Brot":

https://www.google.de/search?gs_rn=27&gs_ri=p...

Ein "belegtes Brötchen" ist etwas anderes; nämlich

https://www.google.de/search?gs_rn=27&gs_ri=p...

Without "open-faced", I would expect a sandwich to have two pieces of bread.
(except maybe in the case of some types of "hot sandwich" that have gravy, jus or some other sauce.)

Danish style sandwiches 
FYI

Dictionary: canape

(I must admit that ours are bigger (ie toast slice size) than the ones that show up in google image search)

Ben canapés tend to be party food... (I understand not in Switzerland...)
look at French bread sandwich 
imo a sandwich is not necessarily limited to specific type of bread

Die Unterscheidung belegtes Brot / belegtes Brötchen, die einige hier geltend machen, ist auch nicht für den gesamten deutschen Sprachraum gültig. In Österreich sind belegte Brötchen kleine belegte Brot-Stücke (etwa in Streifen geschnittene Scheiben), und in aller Regel ungedeckt. Was den meisten Deutschen ein Brötchen ist, heißt in Ö. Semmel; wenn die "belegt" wird, wird sie eher "gefüllt" (und kommt dann wieder weitgehend geschlossen daher).
Wissen wir eigentlich, von was für einer Gattung axirueg spricht / englisch sprechen will?
Das eine wäre mit open-faced sandwich wohl hinlänglich übersetzt, das andere könnte - wenn die beiden Hälften nicht wieder aufeinander gesetzt worden sind, sondern einzeln gereicht werden - eine open-faced roll / ein open-faced bun sein. Aber als nach dem Füllen wieder Zusammengeklapptes? Vielleicht ein panino?

AE is often very creative in these matters; we have the bunwich

If E_S's distinction in #9 is right (*f5* except for Austria),

belegtes Brot - slice of bread with something on top
belegtes Brötchen - filled roll, mini-sandwich

Even with the word 'open-face,' I would expect a sandwich to have a second piece of bread (or the top half of the roll) so that you could put the top part on top and hold it between thumb and fingers. To me the open-face part refers mainly to how it's served on the plate, namely, not yet closed up.

A canapé is something different, typically smaller, more like a Häppchen. Little filled rolls could be served as one kind of snack or appetizer, but in general when you picture canapés you think more of something like little crackers or toast triangles with a spread or other topping.

re #21: IIRC, a panino is typically a hot sandwich, pressed in a sandwich press that's like a little two-sided mini-grill, with some cheese inside that will melt. And I'm afraid many Americans might call it a panini [sic].

here the steak sandwich illustrates that all kinds of bread can be constructed into a sandwich... If you tell your tourists they get sandwiches, they will expect two pieces of bread with a filling - make it German Sandwiches and anything goes...

How about Subway? They call their stuff sandwiches, and they are clearly made from what I would call rolls (or in German Brötchen), not from slices of bread.

http://www.subway.com/Menu/MenuCategoryItems....

You would get very much the same stuff in a German bakery, maybe with a few more traditional varieties of rolls. Sometimes they are open-faced, but more often they are not. I would call both of them "belegte Brötchen" (the open-faced variety might be called "halbe belegte Brötchen").

So I'd just go for "sandwich".

Bei den auf der Subway-Website von #25 gezeigten Kreationen handelt es sich aber nicht um Brötchen (= Semmeln), sondern um Baguettes.