That might be too late, since everybody tries to find a garage to change winter tires, especially in OTTAWA. If your winter tires have their own rim, and you know to do it yourself, then yes, when snow starts to fall.
I have changed my winter tires two weeks ago (temperatures in the morning and after work are below 10 nowaday! And I don't want to WAIT for hours to have them changed.)
From December 15 to March 15, all taxis and passenger vehicles registered in Québec must be equipped with winter tires. This requirement also applies to rental passenger vehicles in Québec.