IEC (Working Holidays, Young Professionals and Co-op) program requires its participants to have a proof of travel health insurance covering medical care, hospitalization and repatriation for the whole duration of their IEC participation. Even though most provinces enable IEC participants to enrol in their provincial health plans, having a provincial health car is not enough since it does not cover repatriation (returning to your country in the event of severe illness, injury or death).
When you arrive at the port of entry, the CBSA officer may ask you for proof of health insurance and you must be ready to show a proof of health insurance valid for your entire stay in Canada. Even though you might not be asked to present a proof of your travel health insurance at the POE, you should not take any risk. If you do not have travel health insurance for the whole duration of your IEC participation, you might be refused entry. If your insurance policy is valid for less than your expected IEC stay, you might be issued a work permit that expires at the same time as your travel health insurance.
Finally, please note that if you do not receive the total time your are entitled as per your country agreement because of your lack of health insurance, you will not be allowed to extend your work permit at a later date.