I love Montreal. Definately one of my favorite cities in North America.
Take a walk / hike to the top of the mountain (mount royal). That's a must for any trip to the city. The views are amazing.
St. Denis and St. Laurent streets rock my world. I could wander those streets for hours.
Old Montreal is awesome too.
I went to Olympic park once. It was OK. The biodome was pretty cool and we also went to the top of the "tower" in Olympic stadium. I'd do this option (tower) if you are pretty bored only.
Have a great trip man. If other stuff comes to me i'll mention it.