We were looking for a bit of a hike and had read of the chalet and belvedere atop Mount Royal, so we walked from the nearest Metro Stop near McGill. Unfortunately the signage on the mountain was very bad and when we got to the chalet it seemed the belvedere was farther up- no, it is actually the patio in front of the chalet and the signs had us scurrying all over the mountain looking for the belvedere. Portions of this park are slated for renovation so that should help. The view, when we finally stopped to look at it, was worth the hike.
Walking up the mountain is strenuous but shouldn't take more than 45 minutes each way, so not too bad.

Best view of the City. Also a great atmosphere to take in the sites. I would recommend this over the view from the Olympic Stadium

If you have a car and about 1-2 hours to use up via exercise, and love views and beautiful flowers in August, take a ride up Mount Royal. This is the only real elevated area in Montreal,(if you ride the incline at Olympic stadium this will be verified). At the top of the mountain is an extremely large Lit(at night) cross/crucifix that could be seen for miles. You really can't get to that area without lots of walking but ride up there to see a beautiful view of the city(for free), lots of people exercising and taking pictures, and a beautiful chalet type building with lots of stairs for resting, beautiful flower areas for viewing and just a break from a busy city. I think you need to pay for some parking via a machine and get a ticket to put in the inside of your windshield. We did not do that due to our negligence, but noticed these tickets when we walked past other cars. Elderly people and those who cannot walk about 1/2 mile should probably avoid this area, but a very pleasant spot with great vistas and opportunites for photography. Also very, very clean as all of Montreal is.