I think financially literate people in Canada don't pay anywhere near $200. I've always paid around $50/mo for the last 20 years, without ever going out of my way to shop for promotions, and have been able to have all the data usage I could reasonably use (previously excluded watching videos when not on Wi-Fi, but the most recent plan of a few years has enough data that I no longer need to), plus extra bells and whistles like free roaming in the US. This is with both a corporate plan with Bell the last 6-7 years, and a regular single individual plan with Rogers all the years before that, so wasn't even with a lower cost provider.
There are huge promotions multiple times a year because the competition is fierce between the top providers. When long-term contracts that subsidized phones were still around up to a few years ago, the buyouts to switch providers were so aggressive that you could end up with an extra few hundred dollars in your pocket on top of a new phone every 2 years when switching providers, or staying with the same provider and getting the loyalty/retention department to match offers. Yes, there may be better deals to be found down south sometimes, but not by enough of a margin to deal with cross-border banking, currency conversion, and much worse consumer protection laws for most people.
Yes, additional competition might potentially help drive prices down, but the low ROI on the huge amount of infrastructure required for such a small population might also result in worse economies of scale for all players resulting in the need to cut corners on coverage or service quality to remain competitive.
Also, I'm not convinced coverage is better down south. Anecdotally, I seem to hit way more deadspots driving down I5 through Washington and Oregon than I do on Highway 1 across BC to Alberta despite having much larger swathes of populated areas. I'm also shocked everytime I go to New York and get zero cell signal in every subway station including near Wall Street, when every underground transit station in Vancouver has coverage (admittedly Toronto does not have this though).