It seems Vancouver and NYC are the most shot cities

Agreed? What is the connection with the two?

Lots of interesting subjects maybe? NYC's got the massive cityscape and blends a lot of different cultures together which is always a treat to shoot though it's been pretty hard lately with all the crackdown on what you can/cannot shoot. As far as Vancouver goes, you can't go wrong with any scenery unless you take a wrong turn and wind up on east Hasting's which will certainly provide some interesting subject matter! I always enjoyed the drive from Vancouver to Whistler in the spring or fall which had some pretty awesome views.

Toronto doesn't have much interesting shooting aside from motorsports for me.

I think it has to do with an active downtown scene and the ability to live, work and play within a small area. More or less you could live in either city without having a car. Therefore there are a lot of people walking and the area is conducive to walking. There are a few other US cities that are somewhat similar like Chicago, Atlanta or even San Diego. These town have a vital (or revitalized) downtown that is now hip and active.

If you live in an area like LA, Las Vegas or Phoenix there is no way to live without a vehicle. The distances are just to large to travel any other way.

The other item to consider is the weather. When the weather is nice in Vancouver or NYC it is really nice.