There are lots of fun things to do in Montreal, I will list some and include sites for details of events and prices but make sure you do not miss the JAZZ Festival which is on now until July 6, 2010:
Old Montreal - Cirque De Soleil
Casino - F1 Track around it
Saint Catherines - Shopping
Crescent Street - At Night
The best site that answers your question is :
Good luck and have fun!
Montreal Botanical Gardens
Montreal Museum of Fine Arts
While you're there, screw Bret Hart out of the WWF Championship.