I just finished my first winter of bicycle commuting. I used a mountain bike (actually 2 but won't go into details). The bike I used was what the neighbour was throwing out when my son picked it up several years ago so it was a beater and it was free. It happened to be a Giant. Just remember, you're going for stability and handling not speed.

Just a few checks to make sure the brakes and gear shifting was in proper order and with studded tires a bell, mirror, rear rack and it was ready to go.

My limitation is 5cm of fresh snow. Just can't pedal through it until after it's been packed down. So make sure your tires are wide enough or check the route you'll be taking. Will it be busy enough for motor vehicles to pack and make tracks for you after a heavy snowfall? Will there be pedestrians packing and cutting trails for you in Multi-Use-Paths?

I was considering a fat bike but I just can't justify spending $500 or more for a new bike that's going to be subjected to the worse conditions and then risking it getting stolen. So if you can find a used mountain bike with forks that can accommodate 3inch or wider tires, go for it.