Your phone should work in Montreal as Bell and Telus have their new networks set up there.
ALTHOUGH I was just in the states this past weekend with my Telus Iphone 4 and had one hell of a time getting a carrier. I hooked up to Cellular one and AT&T for a while but could not receive calls. I had to go into the general>networks and let it search for a carrier and then reboot in order for it to see the carrier.