As a Canadian, Canada needs way more people for how much habitable land we have.
What a coincidence, this is exactly what the Century Initiative wants. Toronto would go from 8.8 to 33.5 million people. Vancouver from 3.3 to 11.9 million.
BC for example is pretty much all mountain and has dammed and flooded many of its habitable river valleys.
In the Prairies the land is already valuably used to export food across the world.
In other parts of Canada it's muskeg and inhospitably cold.
The other thing that everyone always forgets about is that all this "free" land out there is not at all free for the taking: it is under land claims by First Nations. These longstanding unresolved issues will need to be resolved before people can start cutting down forests somewhere and laying out a new main street.
There's plenty of room for more Canadians in the parts of Canada that are already developed, but not a terribly compelling reason for expansion beyond that.
Mars, Moon, and some places on Earth defnitely are not habitable (unless very supported), but calling most of the Canada "unhabitable" is more than a stretch.
And that's precisely the problem! Carbon footprint per capital is very high in Canada and for remote and colder locations it would be even higher!
That remote part of Canada would still be an issue though because it doesn't look like there are any train lines, major rivers or sea access.
[0] https://ourworldindata.org/environmental-impacts-of-food?ins...
[1] https://theconversation.com/suburban-living-the-worst-for-ca...