As a Canadian student, here's my perspective:
If you're going into life-sciences with an intention to go into med school, I'd definitely NOT recommend UofT. Yes, it's ranked highly, but rankings are NOT everything. It's super competitive, and your GPA will not be as high as it would be if you went to a smaller university (& GPA is the important factor in med school admissions). UofT does not focus on undergrad education at all, and you really would not be getting the education you'd want there.
On the flip side, as an international student, you'll probably fit in really well in Toronto. However, the same can be said for Montreal and Vancouver as well, the two other largest and most multicultural cities in Canada. Being big cities, the social life is about the same as well, and the same could probably be said for weather (although winters in Vancouver are milder than those in Toronto and Montreal). One thing to keep in mind about McGill however, is that if you're looking for a part-time job during the school year, unless you speak French as well, you'll be hard-pressed to find one.
if you're going into med school in Canada (after undergrad), I'd highly suggest you look at other unis as well, because WHERE you get your undergrad degree will NOT matter. Nonetheless, other well-known/top-ranked life sciences/pre-med programmes would be McMaster's Health Sciences (super competitive) or Life Sciences, and Western's Biomedical Sciences.
Hope this helps & remember, rankings are NOT everything, especially for undergrad!