The US's comfortable position isolated by oceans is often used as an explanation of how it could dominate militarily as a world superpower (easy defenses). But Canada shares the same advantage. Did Canada simply choose not to focus as much on empire building, or were there other factors that would give the US the clear advantage?
While Canada and the US have the same basic advantages in regard to geographical isolation by sea, the land they hold is not equal.
From the beginning the Canadian settlement were too far north to attract large numbers of settlers. Long harsh winters with short growing seasons don't bring in the prospective farmers, especially when there's better colonies to move to.
The American colonies were better placed on the east coast and attracted the vast majority of settlers. These settlers developed the colonies into viable cities that would attract more settlers who were not farmers but skilled city folk.
After the American revolution, Canada was reenforced by American Crown loyalists but the weight of the momentum west was already started. Canada started on the periphery of good land and it stayed there. Never having the population to push south.
As a little side note, my own family came to Canada in 1821 from Scotland because of free land grants. But you get what you pay for, the land was no good so the father of the immigrant family moved to Massachusetts to make a living and abandoned the family. When his son came of age requested a change of the land grant but the new plot was just as bad and by the 1840's had moved to Illinois.
This family anecdote doesn't prove anything on its own but gives a little snippet into how some settlers had to leave Canada because of bad land. And it's this population boom for the US that contributed to its Super power status over Canada