Upvote:6
If the cruise is a closed-loop cruise (i.e., it departs and returns to the same port in the US), then you don't necessarily need a passport:
U.S. Citizens on closed-loop cruises will be able to enter or depart the country on the cruise with proof of citizenship, such as an original or copy of his or her birth certificate (issued by the Vital Records Department in the state where he or she was born) and, if 16 or older, a government issued photo ID. ... The United States does not require you to have a passport. (A Consular report of Birth Abroad issued by the Department of State or a Certificate of Naturalization is also acceptable.)
HOWEVER, it is possible that one or more of the Caribbean Islands on your itinerary, does require you to have a passport to enter their country. In that case, it is very possible that the cruise line will require you to have a passport to board, even if it is not a U.S. requirement.
Note also that Canada will accept a birth certificate as proof of citizenship for entry:
If you are a U.S. citizen or permanent resident, you must carry proof of citizenship such as a passport, birth certificate, a certificate of citizenship or naturalization, a U.S. Permanent Resident Card, or a Certificate of Indian Status along with photo identification. If you are a U.S. permanent resident, ensure you carry proof of your status such as a U.S. Permanent Resident Card.
I would check all of this with the cruise line ahead of time to confirm that you'll be OK to board the boat without a passport. I'm sure that this situation is not infrequent among cruise passengers.