SIN and Health Plan cards are valid for life unless specified on the card itself. Once you've received your SIN card, there is no limitation beyond jobs only available to those who are Canadian Citizen (if you are not one yet)
Note: If you are a permanent resident and do not have a PR Card, you MUST visit the Consulate General of Canada in Hong Kong to get a travel document that will allow your entry to Canada. Otherwise, airliners have the obligation to deny you from boarding the plane. http://geo.international.gc.ca/asia/hongkong/immigration/tdpr-en.asp