The biggest drain, especially in cases like California, is illegal aliens. They are given the same emergency care as citizens; which is also paid for by the state if the alien can't pay.

So you have huge communities of undocumented illegal aliens who may or may not speak English (they mostly don't), who probably are not paying tax (because they work for cash) and can't afford insurance. They get really sick too. I know this because one of my brother's groomsmen is living in LA and attempting to organize state run health programs for them; because it is vastly cheaper than not running health programs. Personally I think it would be cheaper still to kick them all out ... but California.

In Australia if an alien just makes up a SSN (Australians have a "Tax File Number" but it is the same) then the tax contribution are paid for by the employer and they never get a tax refund. They are also not entitled to any government services that are paid for by tax. So the Single Payer Government Insurance Scheme (Medicare) which pays for all of an Aussie's medical costs is not available to them. If they go to a government hospital (almost all of them are) then they must pay for the costs of their own treatment.

Don't get me wrong, the treatment is affordable compared to the USA. A night in hospital with a high level of care is something like AU$1000. In the USA it would be a miracle to pay less than US$15,000 and pay US$40 each for a paracetamol tablet.

The Australian Taxation Office (ATO is the Aussie IRS) won't look to kick out working aliens; because they pay a lot of tax that they don't spend. Hospitals won't report aliens, because doing so would stop people from seeking care, which results in ambulances and emergency care, which costs 5X. Mostly the small number of illegal aliens here are from English speaking countries like the USA and the UK. The first time they are arrested for anything they get deported.

I think the biggest hurdle to sorting out the USA's health care system is that illegal immigration really has to be solved first.

The UK has bulk, legal immigration, and as a result the UK National Health Service is buckling under the strain. People arrive from overseas with (comparatively) poor health, later in life (30 or whatever) and require a lot of care, all in London. It doesn't matter how much money the UK government dumps into the NHS, it is never enough.

As for Canada, I am sure that there are minority populations that require disproportionate health spending. For example Native Canadian communities have high unemployment and low health. They don't pay much tax and they do require a lot of care.

In general a WELL RUN Government, Single Payer Health Insurance plan is more efficent and delivers a better service ... but how you get there from where the USA is now is impossible. It just can't be done. Even if it was done, I don't think that the controlling factions of US politics would have any interest in running it well.