Your question presupposes that folks of Chinese descent in Canada are immigrants. There's been a strong Chinese community in the area since before 1900. As a comparison, my great-great grandparents emigrated from Italy in the 1920s. It's quite typical for Canadians to retain their cultural identity and ancestral language post-immigration; the notable exception being indigenous peoples who were forced to assimilate. Where my family immigrated to the US and abandoned our language, I later immigrated to Canada, I was shocked to discover an Italian community where folks are still raising their kids to speak Italian after generations.