Climate, Toronto and Montreal are basically the same. You only need to worry about winter though, as spring/summer/fall are VERY nice. Especially spring! As for Winter, if you watch "Game of Thrones," think "Castle Black."
I live in Toronto and I've been to Montreal last week. It's VERY nice there. Food is 10,000% better. Even McDonald's tastes better in Montreal. However, French IS their first language. I also encountered 1 woman who can't speak English at all. So keep that in mind. I myself want to live in Montreal but I do not speak French. Things are also slightly cheaper in Montreal. Parking is MUCH cheaper. I heard rent is also cheaper. The city is much much more beautiful than Toronto. I did not encounter any racists or rude people there. In fact, they were very friendly.
Toronto is a much, much bigger city though. Perhaps even if you combine Montreal and Vancouver, the GTA, as a metropolis, is huge.