Another vote for .204. 32 gr V-Max leaves pencil sized holes with no exit. Also can see impact through scope. Laser beam out to 400 and fairly good barrel life. Stock Tikka is tough to beat for a light walking rifle.
Interesting thread. I live just south of OP in same province and hunt and shoot in similar weather. Not out hunting in quite that extreme but was able to get my first quadruple coyote on one stand last year in about -35 C. Had to snowshoe in 2 miles to get to the river due to all the snow we had...