ride a heavy fat steel bike with both front and back suspension and low tyre pressure and tyre treading for slowing the speed. Sit upright and keep the seat position low for inefficient pedalling.
If the snow cover isn't very thick (just a couple of inches on top of road) a thin tire will cut through it better to get to the road.
There is likely ice under that snow so you need studded tires like these:
http://www.chainreactioncycles.com/ca/en/schwalbe-marathon-w...
Note they come in various widths: down to 35mm (commuting road bike size) to 2 inches (MTB).
I would take these in the 40mm width over the other sizes for commuting in the snow.