In summer you want to hang around the Plateau for all the sidewalk cafés, especially on St. Denis Street. The Old Port is pleasant to walk around. Rent a bike and ride along the Lachine Canal to Atwater Market. Spend an afternoon in Park Lafontaine or go to St. Helen's island and bike around the park. If you want to go to the "beach", Cap St. Jacques and Oka have pleasant lakes with lots of young attractive people.
For winter: find a good bar and lock yourself inside. It's cold! about 6 years ago