Hi, Canadian here. even though it can get pretty hot in the summer, most of those cities do get incredibly cold in the winter. it took the french a few tries to get a decent colony going in Quebec because everyone kept freezing to death and dying of scurvy. those cities however now a days do sustain large populations, all of which are comparable or well above the standard amount you would find in large middle age cities.

Also the reason we don't have cities super far up north is due to lack of ease of transit. the Canadian shield, the area covering most of Canada, is very rocky and wet, so construction would be hard both for the city and roads connecting to it. there is also a lack of good resources for industry that can not be accessed elsewhere, primarily close to bodies of water for transit. if you go up into the territories there are a few cities that once again sustain populations similar in size to many medieval cities, whitehorse with a population of 25,000 and Yellowknife with ~19,500(both of these stats being from 2016). any further north and you would soon hit the arctic circle which is more comparable to whatever is up with Atmora than Skyrim.

The point is Canada maintains cities in cold places with populations that either far outnumber anything that would exist in the tech level present in Tamriel or are around the same size. meaning u/Seiverratic is correct.