Yeah.
I don't think Canada is overcounting by very much. I think we claim to have about 37 million on this massive portion of the planet. I have a good feel for the size of my hometown of Vancouver BC, which is supposedly about a million or two (depending if you count the nearby burbs), and I think it's about right.
I've never been to China or India, but know people who have, that I trust. I believe that it's quite densely populated there... but I'm with you, I doubt it's 1.5+ billion each.
The other side of the equation is resources. Yes, they are in many ways finite. But not as scarce than we've been made to believe. Same with technology, a lot of that has been held back from the commoners.