For a Sudbury winter, I would go with the fatter rather than skinnier. If you can afford studded tires, I would go that route. If not knobbies will work for you. You don't need a drop bar, no advantage in the winter. I have done both ways when it comes to gears. Last year I used a Surly Singulator and went single speed. This year I am going to try a derailleur again but I don't have to deal with as much snow as you do.