Fundamentally housing pricing isn't about affordability, it's about supply and demand. The reason for the high prices in Toronto and Vancouver is because we aren't building housing, and the infrastructure to service it, fast enough. People want to live in Toronto and Vancouver so filling the units will never be a problem. If there was ever a housing glut we can just open the crack in the immigration door a little wider and we would have a zero vacancy rate again.
The real problem is that the economics of "the American Dream" - that is buying a house at thirty, having it paid off by fifty and retiring at sixty-five to travel the world, is not a sustainable model anymore in many urban markets. I suspect those people talking about "cooling" the market are really using it as a code that means tipping the playing field so baby boomers (read voters) get a larger piece of the pie, at the expense of REITs and international investors.
Of course the other side of the housing cost vs. income equation that no one is talking about is income. If society/the government wanted to fix the problem without interfering in the market they could raise wages so everyday people could compete with foreign investors on a level playing field.