Montreal: Authentic, francophone community, sort of tumblr-y.
Toronto: Big new city, a lot of immigrants, clean.
Vancouver: A lot of greenery, cool harbors, small city.
Montreal easy, and I've visited all of those cities.
Montreal for its culture and historic parts of town + nightlife.
Vancouver is gorgeous for its cities, proximity to the water and mountains.
Toronto is an amazing city but I find that it lacks something, not sure. Still love it though.