The questions you asked are really depending on individual's situation. Why I want to talk to you directly is that I am trying to confirm your situation is similar to mine. If it's not, what I say here could be a misleading to you!
Anyway, here comes the answers to your questions if yours is similar to mine:
1. It doesn't matter where you are. Just send a letter to Canada Revenue to state that you've left for HK and give them your new address.
2. No, you can stay as long as you like if you keep your Canadian passport valid and you have the valid working visa in HK.
3. No, as long as you have a valid Canadian passport, you can return to Canada at anytime at any port back to any city and absolutely at your favor.
Anyway, here comes the answers to your questions if yours is similar to mine:
1. It doesn't matter where you are. Just send a letter to Canada Revenue to state that you've left for HK and give them your new address.
2. No, you can stay as long as you like if you keep your Canadian passport valid and you have the valid working visa in HK.
3. No, as long as you have a valid Canadian passport, you can return to Canada at anytime at any port back to any city and absolutely at your favor.