Mortgages in Canada have to be renewed every 2-5 years. Rates renegotiated. There have been rumblings for years that there are a huge number of homeowners who would be unable to pay their mortgage with a 1% increase in rates. Now we've seen rates go from 1.9% to 5.4% in a year, with more rises to come.
All the while, we've had a housing bubble going on. My condo at one point had doubled in price from what I bought it for 7 years ago, based on neighbouring units for sale (and sold). And it was already inflated in value back then.
How many homeowners were barely able to afford a $1.5m home[0] 3 years ago at rates of 2%, and are paying $6,300/month, and in the next 6 month will renew their mortgage at 5.4% and be unable to afford $9,000/month?
Those houses will go up for sale, and that is how bubbles pop.
[0]What, you think $1.5m is too much for a house? Take a look at realtor.ca and browse most neighbourboods of Toronto. That much won't get you much, for the moment. Also, it's CAD so take 30% off.