Canada Mortgage and Housing Corporation says Toronto, Ottawa and Montreal most at risk.
The country's housing market went from a moderate to a high degree of vulnerability in the second quarter of the year.
Canada Mortgage and Housing Corporation (CMHC) says the change is due to factors such as price acceleration and overvaluation throughout the country.
The rating is also based on overheating and excess inventories.
Cities with the highest risk include Toronto, Ottawa, Hamilton and Montreal.
While Niagara doesn't get a vulnerability rating, the CMHC says the area is experiencing strong price growth.
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