Actually, in principle larger means more markets and labor supply and more clout on the world markets. Furthermore the US has more usable land, and Canada's vast distances with low populations increases their expenses vs the US.

And indeed the US does have a higher per capita GDP. But because it's concentrated in so few hands, most Canadians are better off than most Americans.

As someone else in the thread has already pointed out, which one do you think will be less stressful and noticeably easier to manage - deciding what to do for dinner for a group of 3 people vs. a group of 30 people? It is much easier to converge on a decision that will leave everyone satisfied when you have 3 people. While with 30 people, it is almost guaranteed that there will be a few people who would be left unsatisfied, a few satisfied, while the remainder will just end up being "ok" with the compromise.

The distances between are a contributing factor.

But that would apply even more to Canada then, no? Or did I misunderstand what you mean?

Not with smaller population size :). Maybe colder climate makes people happy?

Not really, as it depends on distribution as well.

They actually aren't that different (distribution-wise) in many places, although obviously Canada has a lot more parts where people are really spread out. Because most of Canada's population lives in the southern 10% or less, there are many regions where density of infrastructure & people looks kinda-sorta-the same. Obviously there are exceptions, and only one large city, etc.