Filming in Canada (Vancouver, Toronto, etc.)

[Big Disney Fan]

I have read that many movies and TV shows set in places like New York City or San Francisco or wherever were actually filmed in locales in Canada, such as Vancouver or Toronto.

My question is, how can they make the different cities look convincing? Don't Vancouver or Toronto actually have locales of their own that would ruin the effect?

I had read an article where they would try to make Toronto look more like NYC by throwing in countless taxis, but what about the buildings? NYC is not home to the CN Tower, I don't think.