I looked up the Poconos and it looks like Toronto is slightly colder and Montreal would be a bit colder than Toronto still.
December can be somewhat variable in these cities: sometimes there is no snow and it can be mild (everything being relative: mild in Dec. is still generally under 50 F), and there can be little snow.
This year it appears that temperatures are going to be seasonably cold. Here are the forecast trends for the next two weeks:
14 Day Trend: Toronto, Ontario - The Weather Network
14 Day Trend: Montréal, Quebec - The Weather Network
Pretty much all below freezing for both cities. Montreal has already received a lot of snow which will likely stick around. Toronto has received some dustings but will likely get more (based on this forecast) between now and Christmas.
You can also get cold snaps at this time of year that will drop the (generally night time) temperatures down to 0 F or lower, but this does not happen every year.
My best advice would be to bring any gear that you would wear for going skiing. You may not have to wear all of it (esp. pants) for just walking around town during the day (both cities have subways and extensive underground networks), but if you do want to spend an extended period of time outdoors or if you want to partake in winter activities you will likely need the ski-type clothing.