Obviously there is the housing crisis, but housing prices are crazy in most huge metros like this. The best way to combat this IMO is to make it easier to get into the city from outside so people can live further away without worse commutes. And the only way to accomplish this is to drastically improve the public transit in and out of the city.
I recently moved out of Markham, from my old place to union station it would be 1.5hr bus ride, a 1hr car ride with traffic, and a 20min car ride without traffic. Lowering that bus ride would directly lower the with traffic number too.