I have noticed most UK/USA residents don't seem to have this problem but as a Canadian living in Saskatchewan I have had trouble finding providers that even sell insurance over 1 year. If you actually read there policies almost none sell to Canadians for over 365 days. And if they do then its for a much reduced coverage such as $20,000 instead of $1,000,000.
Some providers say they will insure you as long as your provincial health care is still active but I have talked to Saskatchewan health services and they will not extend there coverage after 1 year of being out of the country. Many Canadian providers don't even do over 183 days.
An example of this is the very popular World Nomads who says this on there FAQ for Canadians.
If you are traveling for an extended period of time, you would need to take out a 6 month policy initially and then extend for as long as you need, in increments of up to 6 months at a time. Please note that at present the maximum total duration we can insure you for on the one trip is 365 days and you should also hold valid provincial health cover for the duration of your extension. If you do not have valid provincial health cover for the full duration of your trip, your aggregate limit for all Emergency Medical and Dental Benefits will be CAD$20,000.