Your question is very subjective.... It all depends on what are your parameters for judging a city.... If it is employment opportunities and jobs, without a doubt Toronto it is. Vancouver is usually a choice for people looking to avoid the dreaded Canadian winters. Vancouver and most of BC is exquisitely beautiful too! But if you chose Vancouver, be warned of winter rains. Some say heavy snow is better than a very wet winter! Calgary was good overall but the depressed oil prices has shaved off a lot of jobs and job opportunities. Calgary by the way is the "sunniest" city in Canada... Nearby Edmonton is also facing a toughened job market.
We wanted to go to Vancouver but ended up in Toronto in June this year. A great city with a lot of affordable satellite townships. Very diverse and multi racial. Almost every second person seems to be foreign born, that may make assimilation easier...
If you have to chose, chose between Toronto and Vancouver...
How should you chose??? Ask yourselves these questions...
Do you have any friend or relative in any of these cities who can accommodate you for a few weeks?
This makes a lot of difference.... Not only financially, but socially as well. First couple of weeks you will just spend time trying to get over your jet lag, make sense of the electrical switches and water less toilets! ;D....... During this time if someone can house you, feed you and once in while drive you around or even explain the local public transport, life will become a lot easier for you!
How scared are you of the winters?
I was scared and let me tell you it does get cold here in Toronto! Imagine we have already had "flurries" (very light snow) few weeks back. But you need to understand few things about the cold. Inside homes and apartments, it is always warm due to the heating. In fact in apartments, it gets unduly warm sometimes! Temps. keep fluctuating... Sometimes it becomes very warm like it was today and a couple of weeks ago it was chillingly cold. But inside, you have no issues. Even outdoors, if you are dressed appropriately, you will find it pretty bearable. More than the cold, it is the wind tha gets you and once you reach, you will learn how to cope with both cold and the wind... You will learn new brands like, Northface, H&M, Canada Goose, Marmot, Arcteryx.... You will see stores like the MEC... Google them for fun! In fact we enjoy the cold now! .... So.... Dont let cold be the only deciding factor... It is not as bad it seems! But if you are 100% sure you will to be able to bear it, chose Vancouver
But if employment opportunities are the deciding factor then Toronto should be the first choice. Once you are able to get a job and gain some experience, then you can always try moving around. But for a start, Toronto is (right now) a better choice...