Canada and USA Residency

Let’s deal with the provincial rules first. All provinces, except Ontario and Newfoundland, require you to actually live in your home province for at least six months plus a day (183 days in most years) in order to be considered a permanent resident of that province, and therefore qualified for provincial health insurance (medicare) benefits.
Ontario allows you to be out of the country for 212 days (seven months) and Newfoundland for eight months without risking loss of your medicare benefits.

If you stay out of your province longer than that, you risk losing your “residency” and with it your medicare benefits, and you will then have to re-instate your eligibility by living in your province for three straight months (without leaving) before you get those benefits back. And you will have to be able to prove that you have complied.
If you overstay that six-month allowance and are seen to be doing so by border agents you will likely be put on a restricted list and denied entry to the U.S. for a number of years. It’s too complicated to list the restrictions and penalties here—just, don’t do it.

If you do overstay and you are seen to be more of a U.S. resident than a Canadian one, you may well be required to pay taxes in the U.S. as well as in Canada and you don’t want that.
And remember most of all, that once you leave your province and enter another country, your medicare benefits stay behind and you become responsible for paying for your own medical costs. You will be lucky if your provincial medicare pays 10 cents on the dollar of any foreign hospital bills you generate.

That’s what out-of-country travel health insurance is for.