As long as you generate/earn your income in HK, you are liable to pay HK tax. But US citizen can claim a tax credit on their US tax payable at the amount of HK tax they paid. Not sure about Canadian Citizen though.
Unofficially any tax that you pay in HK will be "credited" toward your US tax.....as a Canadian, I can say with national pride that the Canadian government has taken the long standing forward step of rewarding non-residents with the gift of NO TAX on foreign based income....lesson..become Canadian...