In order to keep your health card, you must stay in the province at least 183 days every 12 month period (6 months) so if you leave for a whole year, you will most likely lose your coverage. You should ask the health care in your province before you leave. Sometimes it is possible to keep your coverage for longer if you tell them you are leaving and for how long. If you lose it, you will have to register again when you come back and do the 3 month waiting period again.
Now, surely some people will say you can just keep your health card and not tell the health care you are leaving and hope they wont find out but the problem with that is that if they do find out, you could be liable to pay back all of the health care you received while you should not have been covered so it is better to be honest.
Thanks Leon. Very informative post. I didn't know about this that if you leave Canada for longer period your health insurance is gone and you've to register again & wait again for 3 months.