Canada

Honestly, most of Canada's climate is pretty unlivable already. Canada's borders are not the result of a sane process of people deciding where it makes sense for people to live. They're the result of a series of wars where England lost the big one (the American revolt) and the losers of that war settled in the inhospitable territory that England still controlled, mostly what later became Canada.

I don't think a sane planner would say "let's create a country where for essentially half the year no crops can grow", but that's what Canada is stuck with. While Canada's agriculture industry could produce enough calories to keep everyone in the country fed without an issue, the variety would be pretty limited. Canada already imports something like 2/3 of all vegetables and 3/4 of all fruits that Canadians eat.

With climate change, not only is the winter a desolate time when nothing can grow, but summers are becoming miserably hot too. Canada was already much colder in winter than the major capitals of the nordic countries, and Moscow as well. It's also hotter in the summers too. This year it really did feel like things went from way too cold to want to be outside for an extended period, to a brief spring, then a summer where it was also uncomfortable to be outdoors.

OTOH, climate change does mean that Canadian farmers have a measurably longer growing season already. It's still bad, but at least it's a month longer than it used to be.

It really seems like climate change will probably result in more crops being grown in Canada. But, it also feels like it will take away the nice summers too, because they'll go from uncomfortably hot to unbearably hot.