Can I join other countries' nationality if I join Japanese nationality for permanent residence? For example, the United States and Canada

Japan is a nation. People with dual nationality must choose a nationality at the age of 20-22.

However, you said that it is ok to apply for a green card in the United States after becoming a Japanese citizen. The American green card is a visa for permanent residence, regardless of nationality. Get the American green card, or Japanese (or China). Therefore, Japanese nationality will not be revoked after getting the American green card.

If you are a Japanese permanent resident, you are still a person of your nationality (for example, you are from China), and you must abide by the laws of your country. If you are from China, you must give up your China nationality before you can apply for the nationality of other countries, and then you can apply for the nationality of Japanese, American and other countries.

There is an unwritten saying that once you give up your China nationality and want to join China nationality, you will generally not be approved. If your application for another nationality is not approved, you will become stateless. When applying for a green card, Japan will never give up its nationality.