And even then, most people are still choosing to go to the three cities and immediate outlying areas where the most economic influence and possible social connections are - Vancouver, Toronto, Montreal.

This is the real issue. Having grown up in a dot on the map in the middle of the Ontario boreal forest on the arctic watershed side of the Shield, I can tell you that it isn't all that much harder to build infrastructure there than it is further south (sometimes takes a little longer because of longer winters, that's all). It isn't even horrible land agriculturally as long as you take the shorter growing season into account when you're choosing what to plant. So more of the land is usable than you might think. However, people want to go to the places where people already are.