The rules are fairly similar in all provinces, it looks like you can be gone almost 7 months in Ontario before your coverage is in danger.
I was gone 8 months once, and didnt lose my BC Medical (MSP) even though the guy at the BC Government Agent knew I would be gone over 6 (BC regs). Its like all things, you'll have a problem only if you abuse it, or dont pay your premiums.
http://www.health.gov.on.ca/english/pub ... aq_dt.html
includes:
"- you make your permanent and principal home in Ontario"
"- you are in Ontario for at least 153 days of the first 183 days immediately following the date you establish residency in Ontario (you cannot be absent for more than 30 days during the first 6 months of residency) "
"- you are in Ontario for at least 153 days in any 12-month period "
"- Tourists, transients or visitors are not eligible for OHIP coverage. "
"If you are a newcomer to Ontario, or a former resident returning here to live after being out of the country for more than seven months, the waiting period begins on the date you establish or re-establish residence in Ontario. You are also required to be present in Ontario for 153 days of the first 183 days immediately following the date residency is established in Ontario (you cannot be absent for more than 30 days during the first 6 months of residency)."
When you return to Canada, you'll likely need 3 months of private insurance. I went through CAA (Canadian Auto Assn and got a reasonable deal.) Dont forget that private medical insurance qualifies as a Medical Expense on your Canadian Tax return. (As well as nose jobs, boob jobs, laser surgery...)