There are lots of great Canadian photographers other than the mostly dead ones mentioned here. I'm surprised only one person mentioned the "Vancouver School" (Jeff Wall, Ken Lum, Stan Douglas, Rodney Graham, etc). These people did a lot in terms of putting the medium photography on the map in the art world back in the 80s. For more recent stuff, I'd recommend checking out Janieta Eyre, Carlos and Jason Sanchez, Ed Burtynsky, Jakub Dolejs, Kevin Schmidt.
A lot of galleries around Toronto show contemporary art photography. Unfortunately if you want to see the work of more established people like Jeff Wall, your best bet is to travel to Europe or the USA.