I'm in Toronto. Easy decision for me, I was moving from a big city in the US to a big city in Canada. And my job moved me to Toronto, so that was a no-brainer.
The Greater Toronto Area (GTA) has 8 million people, which is about 25% of Canada's population. Lots of jobs and things to do here, and there are tons of immigrants getting started here.
Also, if you're not used to the cold, Toronto or Vancouver are probably your best cities to get used to it. The other parts of Canada are MUCH COLDER...
As I write this, Toronto is +3 C, Ottawa is -3 C, and Winnipeg is -4 C. Vancouver is a balmy 8 C . Edmonton is -7C...