In Montreal, my favorite place is Dieu du Ciel! They are brewing quite a lot of different kinds of beer, and have success in each. The Belgian ABT of this place is called the Rigor Mortis ABT which is quite fantastic. This is not Belgian, but the Pêché Mortel (Imperial Stout) is fantastic (voted the best beer in Canada on ratebeer) and the Aphrodisiaque is wonderful (cacao+vanilla stout).
Your friend can go to these great places for beer in Montreal (these are brewpubs) :
L'Amère à boire
http://brouepubbrouhaha.com/ (Specialized in Czech's Pils, but good beers overall)
Benelux :
http://www.brasseriebenelux.com/ (Never went, but heard a lot of great things)
Brouhaha :
http://brouepubbrouhaha.com/ (Although, when I went there, there were not a lot of choices. Still, the atmosphere is great and weird at the same time, as the pub kept the decoration from the tavern who was there before)
Dieu du Ciel :
http://www.dieuduciel.com/ (Greatest brewery in town)
Le Cheval Blanc :
http://www.lechevalblanc.ca/ (Choice rather limited there)
Le St-Bock : Great Belgian imported beers selection (although, a bit pricey) + Great tap selections of Quebec's beer. Really a great place.
http://www.lesaintbock.com/
Vices Versa :
http://www.vicesetversa.com/ (not a brewpub, but have a great selections of Quebec's beers)
The Saint-Bock also have a lot of Belgium's imported beers (Rochefort 10, Kaiser Blauw, St. Bernardus, etc... if you're ready to pay)
As for stores...
Keep in mind, in Montreal, you don't have a lot of choices as the state has the monopole in alcohol beverages. Which means Quebec decides what beers he imports, and what you can buy. Sure, you can do some private imports, but you have to do it by the government and at the government's price. So when you have a store specialized in beers... well, that store mainly has Quebec made beer. You won't find American beers, nor Belgian beers, nor Canadian beers in general.
Now, in the beer stores (there's some stores in Montreal specialized in Quebec's beer) area, I would recommend:
http://www.depanneurpeluso.com/
http://www.yellowpages.ca/bus/Quebec/Montreal/Depanneur-Simon-Anthony/2240897.html (This place is ugly as hell, very small, but the Quebec's beer selection is good and the prices are great).
Maybe I could search some more stores if you want, but these two stores have a great selection. Keep in mind, an author I read about Quebec's beer once said that the province of Quebec has the greatest breweries in the world (yeah, that's debatable), but also the worst breweries. So I would suggest to your friend to
never buy beers from these breweries : Breughel, l'Alchimiste, Multi-Brasses, Le Grimoire. They can sometime do some good beers, but overall, I prefer not to drink from them. Especially Breughel who has a very bad reputation for selling infected beers...
While these are very good breweries : Dieu du Ciel!, Simple Malt, Microbrasserie de Charlevoix, Microbrasserie de la Nouvelle-Orléans, Brasseurs et Frères, A l'abri de la tempête (the Corne de Brume, a Scotch Ale, is truly fantastic), Hopfenstark, Les Trois Mousquetaires (the 750 ml bottles special beers are always great... Baltic Porter, Weizenbock, Doppelbock are really great beers... but the "normal beer" (red, white, black and blond) are average). I must be forgetting some, but... I'm trying to give your friend some starting point to Quebec's beers.
As your friend like belgian beers, I would suggest these beers (in Quebec):
- Dominus Vobiscum Double (A belgian dubbel)
- Dominus Vobiscum Triple (A belgian tripel)
- Dominus Vobiscum Lupulus (Rare... but maybe he can still find some)
- Dominus Vobiscum Hibernus (Same...)
- Unibroue 3-Pistoles (A belgian Quad.) (Which he surely knows...)
- Unibroue Fin du monde (A belgian tripel)
- Rigor Mortis ABT (A belgian Quad.)
I just moved away from there, only thing he didn't mention was don't drink Boreale 
