Don your son needs to pay a visit to the nearest INS office and they can give him a parole document to allow him in and out of the U.S. until he gets his new Green Card. He will need both his Canadian Passport and the parole document. My Husband is a Canadian Green Card holder and his issue can only be resolved by a personal visit to the INS. I would recommend he call to ensure he knows where to go, and that he arrives very early.
The Cruise line is correct. Without a Green Card they may not let him in to the U.S.
Don't ask me how I know this