Most of the low-density population areas aren't covered anyway. By landmass, it's single-digit percentages or low double-digit percentages of coverage (And often it's weak outside of urban/suburban area).

One of the least dense provinces, Saskatchewan, has some of the best pricing in the country because the government has yet to selloff the provincial telecom to private investors. Manitoba too before they decided to privatize and sell off to an incumbent.

And high-density is no panacea for cost. Tall concrete buildings everywhere can mean more infrastructure costs. Especially if regulations require you to fit infrastructure into the facade. Medium-density is the least engineering: Just put up a tower and call it a day. And in Canada, antenna permits are federal. Once issued, local govs can't stop you from putting up your monstrosity of white panels on a midrise or a big metal antenna.

But you don't have to just compare Canada against the USA. Australia or Iceland have rates that Canadians can only dream of, with similarly geo-population situations.