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Were your parents born in Canada or did they obtain Canadian citizenship some other way?
 
They, as my brother and sister were born in Canada. They became US Citizens after my birth. Mother, brother and sister still live in the US.
 
wwillis71 said:
They, as my brother and sister were born in Canada. They became US Citizens after my birth. Mother, brother and sister still live in the US.

You can apply for proof of citizenship, but you don't need to apply for citizenship--because you already have it.