I suppose this should go without saying, but a variety of first-nations people survived the harsh conditions of Canada for over a millennia before either electricity or European settlers arrived (I can provide a source for this if a moderator requests it, but I would hope this is self-evident). I will use the Cree of northern Quebec as an example as it's the area I'm well-versed in. The indigenous peoples did NOT sit indoors during the winter "for weeks on end." Winter was admittedly a time in which conditions were tougher, but the men of the tribe would leave (often for days and even weeks) to hunt or fish. The women and children would stay in huts with wooden structures and thick layers of moss insulation and prepare the meats, furs, etc. Food could be stored and firewood was by no means scarce (this is the boreal forest, after all).

In regards to white Canadians, the hunters and merchants could make their own fires or rely on trade for food or a source of heat. Many of the white inhabitants of northern Canada up until 20th century were involved in the fur trade, and as such, they developed a reliance on the native population.

Sources: -Waswanipi post journals (Hudson Bay archives). -The 1974 documentary "Cree Hunters of Mistassini." Toby Morantz' book Partners in Furs (1983). -Fikret Berkes' Cree Trappers Speak (1989).

EDIT: forgot to mention that the sources of sustenance varied greatly over the seasons. Beaver trapping occurred in winter and spring (the traps I've personally seen implemented rely on creating an opening in the ice near a den), caribou are hunted in the fall, and fishing is generally seen as a last resort. All of this pertains to Eastern James bay Cree; I cannot speak for the Western Cree of Inuit.