"Canada has a universal health care system run by the government that covers all people. Compared to Canada, do you think the overall health care system in the United States is better, worse or about the same?"
The first thing to say is that there's a bit of push in the first sentence of the poll. If most people like the idea of universal coverage (as I'm guessing they do) it's going to make the poll an inaccurate measure of basic public sentiment about Canada itself, since some people might not know that Canada has universal coverage. On the other hand, "run by the government" probably isn't widely regarded as a plus, so maybe it balances out. I guess if you're looking for a poll that gives you feelings about US and Canadian health care contaminated by feelings about government-run universal coverage, this might be the poll for you.
But I don't think this difference is sufficient to account for the difference between the poll results and the American-health-care-boosterism that one encounters in the media. Part of the explanation of that, I think, is the quality of health care enjoyed by the pundit class. People in the media, and most people who you'll find holding forth on the awesomeness of American health care, have the employer-provided health care that's available to educated white-collar professionals, not the absence of health care that's experienced by 45 million uninsured Americans. Rising health care costs are a relatively uninteresting social issue to them rather than an active threat to their well-being.
There's a cartoon I saw on the wall in our department that depicted a man in a Jacuzzi. The caption was, "The system can't be collapsing! The water's too warm."