Livable to what standard? I think you mean “developed” and the country could easily be developed to the latitude of Edmonton or Prince George, it just isn’t because the population hasn’t reached a density that has demanded northern expansion. There’s nothing that makes it inherently un-livable.
The parts of Canada that aren't settled (and aren't actually in or near the Arctic Circle) are that way not because of temperature, but because the soil is almost entirely unarable: Either rocky Canadian Shield, or "swallows locomotives overnight" muskeg (plus infinite numbers of mosquitos).
