Yes you can do it from Hong Kong. You'll need this form:
http://www.cra-arc.gc.ca/E/pbg/tf/nr73/README.html
You can wait till you get a job in here before you file that. You'll definitely want to do it before it's time to file T1, though. If you don't, and you file NR73 later you'll need to explain what happened to you for the years in between.
You don't have to cut ALL ties to Canada neither; I kept my driver's license, SIN card and credit cards. You just need to cancel your Provincial healthcare before you file NR73.