Montreal gaming stores
There are two main places to go. Valet d'Coeur on St. Denis near the Mont Royal metro stop has a very good selection of items and the prices aren't bad either. They also have a pretty awe-inspiring selection of miniatures from various companies, although they get their Confrontation minis from France instead of America so they're all in French, which is an issue for some people. The staff vary between helpful and out to lunch.
Librarie Donjon at 1312 Maisonneuve East is also supposed to be a good place, but I've never managed to get myself out there, what with Valet being so convienient for me and all.
There's also Captaine Quebec on Maisonneuve West, but I don't like it much. It's overpriced, the staff (especially the owner) are nasty, and they polybag their books so you can't browse.
(edit) Also, if you're going to be in Ontario at all during your trip, the prices are generally better there.
