If a person with American nationality, that is, an American citizen, wants to transfer his nationality to Canada, that is, to become a Canadian citizen, is it easier to do so?

First of all, you should know that applying for immigration to Canada has nothing to do with whether you are an American citizen or not. You should apply in accordance with Canada's immigration application regulations. Moreover, American citizens must give up their American citizenship when applying for Canadian citizenship. The United States recognizes dual citizenship, but American citizenship must be the last nationality you apply for. The same is true of why the United States is overbearing on the issue of immigration, so it depends on whether your personal situation meets the application conditions. Having American citizenship is not an application condition.