As mentioned multiple times above, snow tires are mandatory in QC during the winter months, and the Avis vehicles I rented in Montréal during the last 2 winters all complied. Avis charges a "tire management fee" - conventiently throughout the year and not just in winter.

Hailing from a European country where snow tires have been mandatory for decades, I was surprised to find that in most Canadian provinces, they still aren't. It's a difference like night and day and can avoid many accidents.