Although Chinese National DOES NOT allow Dual Citizenship, in your case, however, you still hold both HK and Canadian Citizenship , due to the fact that you are born in Canada BEFORE 1997 turnover to China.
It should be notice that the Basic Law comes into effect in July 1 1997, and under Chinese Nationality Act, a Chinese Citizens does not allow dual Citizenship, that mean, in order to become a Chinese Citizens (by birth, descent or otherwise) you are require to renounce all other Citizenship that chinese national had.
But the key word of the law is "Come into effect in July 1 1997" Which does not affect the citizenship status already obtained BEFORE July 1997, so in interest of fairness, Chinese Government will not ask any person who ALREADY had foreign Nationality to give up their former Citizenship (Which also against International law regarding Citizenship or Stateless status) and those who claimed other citizenship BEFORE turnover would kept its own Citizenship unless declared.
However, i have to say this now, if your parent gain Canadian Citizenship via you after 1997, THEY WILL LOSE THEIR CHINESE CITIZENSHIP FOR THIS ACTION