In fact barely equal to the diagonal length of the country. How much ever one talks about fertile plains, tropical weather being able to support more people, this no is still bonkers to me
A few hundred kilometres south of the area in the article, is a vast clay belt of about half a million square kilometres. It's fertile. You can grow potatoes and oats and the usual garden vegetables up there. Somewhat settled on the Quebec side, and there are farms, but less than 5% of the area suitable for agriculture, is currently used for agriculture. It's a region about the size of France, and there are no large cities, and the total population is about 100,000.
You can even see the Quebec/Ontario border from space in some spots, because the Ontario side is wholly undeveloped: https://www.google.com/maps/@48.7805302,-79.5591059,52996m/