On my short visit these were the best choice of art galleries in Montreal
Parisian Laundry: Janet Werner
It empty when I visited the really 'great' gallery but thanks to the rich publications I was able to get a very good impression of the artists they show.
DownTown: (actually uptown):
Galeries d'Art Contemporain du Belgo
If you only can go to one place in Montreal this is the place to go, plenty of different "level" galleries, little information though. The best time to try Wednesday to Saturday from 12 to 5 pm.
Projex-Mtl Galerie, I met Louis Joncas, photographer and one of the owners. They have an exciting choice of artists like
War is incredible
The friendliness of a Chelsea gallery...
In the Old Montreal one of the few good galleries: Galerie Orange: Sean Rudman
Galerie Pangee: Stephen Lack
and the beautiful gallerina
Also a good place to visit: Librissime, a fine fine arts book shop.