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I'm going to Brazil from Canada, but I have a layover in Chicago. When I do my check-in, do I use my Brazilian passport or my Canadian? Can I show the Canadian passport when going to Chicago and show the Brazilian passport when going to Brazil, since in Chicago I will have to check in my luggage again? I'm confused and I called the place bought my tickets from and they said I can't use 2 passports. Has anyone done it?