Book hotel through HotWire (if you want a bigger room because rooms are guaranteed to accommodate 4 people) or PriceLine (if you want a better deal but rooms are guaranteed to accommodate 2 people)
i stayed at the Intercontiental hotel. Close to old montreal and the entertainment district tho you'll be with wife and child so that doesn't matter to you as much, but it's close to shopping and stuff
It's like a 1000 sq/ft bachelor condo, amazing amenities, and right on St. Denis.... Absolutely amazing. I ended up getting the sweet deal @ http://www.booking.com .... Apparently it was their grand opening week, so the prices insanely cheap as they worked out the kinks.