Each province handles health care and what is or is not covered in their region. There is a "basic" required coverage that is mandated at the federal level, and then each province can add to that coverage. For example, in some provinces, I believe there is no dental coverage at all, while some cover children up to age 12 or age 16.
Here's what happens:
When you are born or move into a province, the government issues you a healthcare card. Whenever you go to a hospital or clinic, if the service being requested is covered by universal healthcare, they ask you for your card. They scan it like a credit or debit card, and then you see the doctor. If the doctor feels you need tests, they authorize them. If they think you need to see a specialist, they recommend you to one. You don't pay anything for the visits. Only for any "special services", such as if you took an ambulance to the hospital, if you requested a private room, if you took the TV rental service for at your hospital bed.
For prescription drugs, that is a bit different. Where I live (Quebec), if you need medication, the doctor prescribes it. You bring that to the pharmacy, and you get the prescription filled. If you do not have a private drug insurance plan, you are covered by the public insurance plan. For that, you pay an annual deductible, plus a certain percentage of the drug costs.
So who pays for the universal healthcare? All Canadians who pay their income taxes. We have 34 million people in Canada. Let's say 28 million of those are paying taxes and the others are unemployed or on welfare. If all 28 million pay $20 a year toward healthcare, that's $560 million in the healthcare "pot". Now not all 28 million will get sick or need a doctor each year. Let's say 20% of the taxpayers did, and 40% of the 6 million others did. That's only about 8 million people. And if the average cost of treatment was $500, that is $400 million spent on healthcare. So a $20 investment by everyone helps prevent one family or person from having to shoulder these costs themselves. And it prevents us from sending another person into bankruptcy and ending up on welfare or homeless, which would ultimately turn contributors to society into burdens on it.
Americans hear the stories of how Obamacare will increase your taxes and add to the homeless issue and so on. Most of that propaganda is coming from the "healthcare-for-profit" lobbyists, the pharmaceutical companies that are making billions of dollars pushing expensive name brand drugs when generic alternatives are available, the insurance companies that are making a mint off doctor's malpractice coverage, or your personal medical insurance that ends up being cancelled the moment you get sick because they claim it was an undisclosed "pre-existing condition". With 300 million people able to cover the costs of healthcare, that's a lot of buying power! And it means you don't have to pay a lot extra taxes to see a big benefit. Taxes could even go down if the insurance and drug companies no longer get to charge whatever they want.
You also hear about people dying while waiting for surgery or to see a specialist. I'm not saying it does not happen, as there are flaws in the system. Canada's healthcare is not perfect. There are indeed long wait times for some services. But a lot of that depends on if you have a family doctor or not (who can expedite your case if they feel it is urgent), and whether your problem is correctly diagnosed.
Here's an example: My father nearly died from a heart attack. He had no family doctor, no history of heart problems. He felt tightness in the chest a few times so wanted to have it checked out. He requested at a clinic to be tested for heart disease in September 2002, and they scheduled him for a stress test and ECG....in April 2003! In March 2003, he was rushed to the hospital with a heart attack and had to have a stent inserted. He spent a week in ICU. The thing is that now when he goes to the hospital for anything related to high blood pressure or chest pains, he is IMMEDIATELY admitted because of his past history.
Now in the States, he would have had to pay for the initial visit, and they may have ordered a bunch of expensive tests, and they probably would have found the issue, but we would also be paying the large medical bill, probably well over $5000. And today he would be deciding which medications he can afford to take (he takes 19 pills a day now) and which ones he would have to skip because they are simply too expensive for him to afford on his pension.
Canadians can indeed head to the States to seek treatment. This is possible if they can afford to pay for it themselves, if they have private insurance, or if the service is unavailable in their home province.