I really enjoyed this "Birthplace of Montreal" museum.
It's built on the area where Montreal started as a trading post. The museum gives you a cheesy movie of Montreal's history, ok movie just cheesy. You then get to walk through the archaeological site underneath the museum. It's very interesting looking at the artifacts of First Nation tribes, Montreal settlers and traders. Walking in a real site is also an experience. Seeing the walls, floors, plumbing, everything is just intense.
There is also an exhibit on Rue St. Catherine. It shows how Montreal became a capital of culture.