Any control that China has over those of Chinese origin living in Canada is through their passports and citizenship. A very large percentage of Chinese living in Canada still hold PR card status since that gives them the same rights as a citizen (other than certain voting rights) and since adopting a Canadian passport would require that they give up their Chinese passport. 
I assume that the 1.5 million figure that is quoted in the article is the number of citizens and does not include PR card holders or the several hundred thousand Canadian citizens who have returned to China and Hongkong.