Why do so few people live in Canada?

This is because of its climate. The northern part of Canada is so freezing that the soil becomes permafrost, this makes vegetation and livestock hard to grow.

Explanation:

You can not simply import a couple of million people into the country overnight - there has to be infrastructure, jobs, schools, etc. Canada IS growing, and it's doing so at a sustainable rate.

Part of the reason Canada isn't as heavily populated as the US is that for reasons of climate, many early settlers opted to live in a more southerly part of the continent. Even the early colonization was mostly in what is now the US.

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