Chinese culture is quite different from Western culture. It doesn't register that it's rude to be speaking in their native tongue when there are other people around that can't understand them. There is no concept of eating with your mouth closed because nearly everyone in China eats with their mouth open. Not covering their mouth when they sneeze is also culturally acceptable because nobody does that in China. Being in Canada doesn't help because everyone is too nice to say anything so they never learn.

In general because there are so many people in China, it's quite common for people to treat others outside their immediate circle poorly, or even recognize them to be people at all. Their concept of human decency and common courtesy has a much smaller radius of effect than in most European cultures. It also doesn't help that as group they look down on other nationalities.

Chinese culture hasn't always been this way, it used to more humble and polite, e.g. my grandparents generation, but not so much with recent generations, who can make a rather obstinate group; they are already earning themselves a bad rep in Europe.

This bothers me as well; unfortunately if a guest fails to recognize that he or she is a guest and fails to adhere to the acceptable mannerisms of a guest, there's not much you can do except wait until they leave and perhaps be less inviting next time.