I think you might as well be asking about favourite hockey teams. I moved from the Greater Toronto Area to Vancouver for a startup and find the areas comparable, and I know a handful of my classmates out here. I found Toronto had a lot of small 10 year old companies masquerading as startups. "Startup Atmosphere!!!!"

In general, there are far more opportunities in places with more people. Toronto, Ottawa, Mississauga, and Waterloo area are quite ideal because you have a few good universities (such as UT and Waterloo), a few good companies (Google, RIM, etc), and what seemingly might be a good startup city (Ottawa) thanks to Nortell and a few big name hi-techs shut down.

I've always asked myself how come big companies like Google, IBM,etc are on the east side and not in Vancouver. I mean this clearly illustrates that there might be more tech workforce in Ontario. So for a startup this could be an advantage. It's just a educated guess and I don't have any facts yet.

On the other hand, there are tons of game companies in Vancouver ranging from online game, MMORPG, PS3, NintendoDS, to online gambling.

There's MS here but they are here to act as a buffer for their engineers pending H1-B.

Some hardware companies Broadcom, PMC-Sierra, Sierra Wireless.

There are IBM centers in Vancouver and Vancouver Island, but they do largely government projects (consulting) instead of R&D like the ones in Markham area.

Speaking about Google, they seem to acquire a handful startups in the Montreal to Ontario areas.