of that

Sure. Nothing wrong with your sentence.

Nothinbg at all. However I might not have used the first comma.

A subtle point... when one amount is near a fixed percentage or fraction of another amount, with which it is being compared, we can use words and phrases depending on whether we wish to draw attention to the smallness or largeness of the amounts being compared:

I spend less than ten percent of my salary on chocolate (I don't think that's much)

You spend almost ten percent of your salary on beer (That is a lot)

Since you are drawing attention to the small population of Canada compared to that of the United States, you might consider writing

"Geographically, Canada is a bit bigger, but its population is less than one-tenth that of the U.S."

I have the feeling that the intent of the sentence was to compare Canada's low population density with the States' higher density, in which case I'd say something like "is only about one-tenth that of the U.S."

Damn that Contrex, he always nips in ahead of me while I sit cogitating an answer. Gotta think quicker. He's right.

Hmm, he posted it quite a long time before me. Must not have scrolled far enough.

"Almost" sits awkwardly there. Better would be "...but its population is only about one-tenth..." or "... but its population is less than one-tenth...".

Thanks everybody! Canada's population is actually a little bit higher than 0ne-tenth of the U.S. population, so "less" doesn't work.

I think Monterey Jack's suggestion works best: is only about one-tenth that of the U.S.

Then Canada's population is not much (or little) more than one-tenth of the USA's.