think about it: 美国不承认双重国籍, Canada 承认双重国籍, if you were born in 美国, you have 美国国籍. if you applied Canadian 国籍, Canada will accept you. If your Canadian 国籍 was not known by 美国, then you are lucky to have "dual nationality", but if your Canadian 国籍 was known by 美国, then you lose your 美国国籍. It's so obvious, otherwise all American will apply Canadian 国籍 in order to have dual nationality.