As a Canadian ex-pat, retiring in Canada or the US is a decision I'll have to make eventually.
I believe that there are definitely people who get Canadian citizenship so for the health care. I think it's something that Canada is sensitive to and they periodically make getting citizenship harder in some cases (i.e. I believe that it recently became harder to become a citizen for people born elsewhere to with only one Canadian parent or to people with Canadian grand parents).
I think that the ethical question is a bit trickier. Ultimately, what your asking is whether it's OK for you to get "free" health care without having contributed to the system (or at least paying significantly less). Unlike the US, Canadians pay for health care through their income and VAT taxes (i.e. it's not free). So, moving to Canada in when you're older (heavy user of healthcare) without paying in during your earnings years could be viewed as being unethical. I think that this argument is probably stronger if it's applied to someone that could pay for their own services by working until 40 instead of retiring at 35.
For people considering this, you might be in for a bit of a surprise for what "free" Canadian health care is like (especially for older people). Since healthcare is a scarce resource it has to be rationed in some way. Here's my opinion on how it's rationed: In the US, it's more supply and demand so you get what you can pay for. In Canada, it's more about using different methods for different patients. My understanding is that if a 25 year old and a 75 YO have the same condition, more resources will generally be expended for the 25 YO.
Anecdotal evidence (arguably not evidence at all): Another ex-pat friend of mine is a doctor in the US. His grandfather (still in Canada) passed away not too long ago. I remember him saying how he would have received far more treatment if he would have been in the US. Instead, he was given more hospice style care (i.e. made comfortable) instead of more active treatment to try to maximize his life span. I'd probably argue that the US needs to adopt this style of healthcare to try to get a handle on runaway inflation in healthcare, but I'm still on the "younger" side and I might be more interested in getting treatment to maximize my life span as I get older. I think my best bet for that would be to be in the US.
Also, I think that it's tougher to find access high quality health care (and doctors) outside of the three big population centers in Canada (Toronto, Montreal, Vancouver). Part of the reason for the care in the example above may be that the patient lived outside of these areas. Living in Toronto and Vancouver is pretty expensive (might be more expensive than living in a LCOL state in the US and buying health insurance). My sense is that it would be easier to find good services outside of HCOL in the US vs. Canada.
Also as someone who moved from Canada to the US, pretty much everything is more expensive in Canada (and there's more tax on top of the sticker price). So, even if you saved on health care your total annual spending might be less if you stayed in the US.
Q2: I don't think God cares about the Olympics, borders, countries, or citizenship. But, I don't have a source with first hand information here.