It's an agreement countries have that when mail reaches them internationally they will bring to destination. The China to Canada/USA is absorbed by the Candian or USA postal service.
China was considered a developing country with cheaper rates for a long time by the Universal Postal Union, an international agreement that sets the rates for postage. The agreement was renegotiated recently so maybe that will change.
Or, hear me out, some services don't have to be profitable, like sending put parcels and letters within a country, healthcare or public transportation. Essential services you know.
Instead of giving money to mega corpos for them to pocket it, we could pay for services that benefit the citizens, just like China is doing for postal services.
My point is that postal service shouldn't be run as a private company that absolutely needs to turn a profit, just like healthcare for example.
Conservatives love to treat Canada Post as a private company because they can then tell everyone how unprofitable it is and must be dismantled and sold off to private interests. And then, it will cost even more for less services
Everything is an evil Chinese conspiracy to some people it's genuinely hilarious, like the whole concept of investing in the manufacturing sector to provide an active economy for a developing nation and basic principles like economies of scale are all just sneaky commie lies and actually the global economy is just a chubby yellow man with narrow eyes twiddling his Manchu mustache and laughing evilly about how his plot to flood the world with cheap goods is going to put hardworking mom and pop American corporations out on the street, after only a few more decades of improving everyone's lifestyle with affordable living.