Immigration and nationality.

At first, immigrants get permanent residents, usually called green cards. With the green card, they basically enjoy the same civil rights as the locals, but you still use the passport of your country of origin, except that you don't need a visa to enter and leave the immigration country. If you change your nationality, you need to change it into a passport of the country of immigration, so that you can truly become a citizen of the country of immigration. If your country of origin does not allow dual nationality, then when you become a citizen of the country of immigration, you give up your nationality at the same time. If dual citizenship is recognized, you can continue to use your country of origin passport.

Canada recognizes dual citizenship.

China does not recognize dual citizenship.