I wasn’t aware that medical care was less expensive on islands.
Yes, the US is big; but as I recall from Econ 101, there’s something called “economies of scale” - the bigger the operation, the more economical it can be to run it.
The US has areas of high population density and low population density; so do places like the UK and the Scandavavian countries. So too does Canada. Those are just factors that need to be taken into account; they’re not unique to the US.
Plus, the US is a federation, just like Canada. That means that you can take advantage of one of the strengths of your system: general design of the system, plus funding, at the federal level, but implementation by the states and municipalities, to take into account local conditions. That’s how it works in Canada, the UK, and essentially in the EU as well. The EU collectively has a larger population than the US, but health care is delivered by the individual nations, with delegation to local governments, through the subsidiarity principle of the EU.
None of the things that you have mentioned are deal-breakers. They are factors to be taken into account in designing a system.