If I were you I will take this few years a good chance for them to learn Chinese in HK.
Find a good local kindergarten with good English standard. And then when you go back to Canada
you can teach Chinese at home. My sister in law
she completed kindergarten before she moved to Canada and her parents did not stop teaching her Chinese so now that she can even read Chinese novels.
Don't worry about English, children pick up language easily when they are small.
Even if you change your mind he still have a chance to study local primary schools in the future.