再次謝謝8大哥的回複，但是，你看到的信息是不正確的。我也看到一些律師說不可同時持美加國籍。這的確是一個法律是不太明確的issue.
引號源來自大使館的回信：
"Dual nationality is allowed by the US government.
She will not lose her US citizenship by acquiring Canadian citizenship.
She must always enter the US as a US citizen"
同時，請大家看美駐多使館的官方website: http://toronto.usconsulate.gov/service/passports-and-citizenship.html), “A U.S. citizen who naturalizes as a Canadian citizen may generally retain U.S. citizenship.” “ Determination of dual nationality can only be made by applying for a U.S. passport or registration, not by phone or mail.”
