Are a lot of people heavy drinkers up where Gunnar is from? If so, is it due to the long winters?
Yes, and yes.

There are actually connections established between long winters and the moonshine drinking of Finns, Swedes and Norwegians.
It gets worse the further east you go, Russians being the baddest vodka consumers of the lot, in what is known as the Vodka Belt, going from Russia through Finland and most of Sweden.

Finns have quite a reputation. They're known for drinking vodka and carrying knives.

YIP
Zack