I bet the majority of the ATI employees were not from the area (nor am I). Heck, 52% of the people in Toronto were born outside Canada, so I bet at least for the Toronto office it's even more diverse than that.
Somewhat funny anecdote: As AMD bought ATI this turned out to be a slight issue for all of us with a canadian work permit (and there are lots of us) since the work permit states the employer you're allowed to work for and in what position. So as we got transferred from ATI to being AMD employers our work permits of course still said ATI. Turns out Canada did not even have a policy about the legal status of all this, so they had to quickly come up with a policy around the AMD-ATI merger.