I work in tech (not Amazon) and live in Seattle, and given the reputation I don't think I'd really want to work for them in this city given the other options we have here.
But if they paid top-notch salary and had great work, I'd seriously consider it as an option when moving back to Toronto. The employment options seem quite limited and I have a hard time justifying a move home if I end up working on less interesting technology and make less than half of what I do here. I'm afraid of my only options moving home being a massive pay cut, boring work, a terrible commute, and being priced out of real estate anywhere appealing in the city. :(
RE: IBM, if I recall most/all of their engineering is in Markham, they don't treat their employees particularly well, and the pay is so-so (though maybe market rates given Toronto).