There's not really that much habitable land in Canada that's not already being used imo.

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.