Interesting plan! As a native of South Africa and a big fan of Canada (visited a few times, best friend from high school lives in Montreal) I can see the appeal of both places :)
In terms of taxes, SA and Canada do have a dual taxation agreement, so that should make things a bit easier:
http://www.treaty-accord.gc.ca/text-texte.aspx?id=102407However, you'll need to talk to a tax adviser to find out exactly what the situation will be - I'm guessing it will depend on where your retirement savings are based.
In terms of SA property, where are you hoping to buy? This will have an impact on your ability to rent it out while you are not at the property. Short term holiday rentals (1 week to a couple of months) are very possible at the coast or at other tourist hot-spots (Drakensberg, near Game Reserves, etc). But, in other areas (JHB / Pretoria) it's a lot harder to do that kind of short term rental.
Health insurance is a tough one. On the one hand, SA has really cheap health insurance that gives you access to world class private health care for in-hospital treatment. Out of hospital (ie day to day costs, visiting GPs, etc) are also very cheap, unfortunately their aren't the same options as in some other countries for getting those expenses taken off your SA taxes (you can claim medical expenses, but the limit is so low that my health insurance maxes it out before I spend a cent on day to day expenses. However, I don't know if such a policy would cover you for the seven months a year you are in Canada and travelling. From my own travels, I know a combination of travel insurance + my normal health insurance provided me with good coverage, but that was for time periods of 4 to 6 weeks. You would need to investigate what would be the case if you where spending 50% of your time outside of SA. Of course, Canada also has a publicly funded health care system, so it's worth investigating what you would need to do to qualify for coverage.
Hope that helps!