It's no more uninhabitable than the uninhabitable areas of China. But it is non-arable.

Most of the eastern half of Canada north of a certain is "Canadian shield" and is granite shield rock with little if any topsoil.

The other half is boreal forest and some of it is indeed farmed to a fairly high latittude (central Alberta where I'm from) but once you get up high enough the growing degree days are not sufficient to grow a lot of crops. It's good for grazing if that. And also fairly arid in spots.

And the rest is mountains, or arctic.