There is a good chance for snowfall in YUL on any given day from November to April. Historical averages don't really tell you much for specific travel dates - a short-term weather forecast does.

As mapleg said, the city and the airport are used to snow and know how to handle it. But snow removal, deicing etc. will still lead to delayed flights, and in the case of massively reduced system capacity, some flights on high-frequency routes (LGA, YYZ, YTZ etc.) will often be cancelled to take pressure off the system.

If you don't want to take a chance with weather-related delays, avoid Canada in the winter. Oh - and BOS too!