Well, Columbus's birthplace is actually a little controversial. Some people say he was born in Italy, other place his birth in Portugal. There are also claims that he was Basque, or even French.
For an interesting read, click here:
http://en.wikipedia.org/wiki/Christo...ational_origin
But even if he isn't American, we have holidays celebrating other foreign nationals... Any particular reason you want to get rid of Columbus Day?