Romance on the High Seas (1948) on Netflix

Wealthy Michael and Elvira Kent, who are celebrating their third wedding anniversary, have never trusted the faithfulness of the other. For Elvira, that suspicion stems in large part from Michael always baling at the last minute from taking an anniversary trip as he always seems to be called off on a business trip for the pharmacy conglomerate where he works which is owned by Elvira's Uncle Lazlo. So when Michael bales again on their planned third wedding anniversary trip - a round trip cruise between New York and Rio de Janeiro - Elvira decides to test Michael's faithfulness by pretending to go on the trip. In reality, Elvira is staying in New York, she who hires a private investigator to spy on Michael. Further, Elvira hires Georgia Garrett, a rough-around-the-edges penniless honky-tonk singer who she meets at the travel agency, to take the all expenses paid trip in her place. Georgia will pretend to be Elvira in every aspect, including maintaining a proper image which means no improper fraternizing with men on board. Michael, in turn, believes Elvira is meeting her lover on board, and as such hires his own private investigator, Peter Virgil, to shadow Elvira on the cruise. Complications ensue when Peter falls in love with who he believes is Elvira but is really Georgia, while Georgia falls in love with Peter, with who she can't have a relationship since she is supposed to be married Mrs. Elvira Kent. A second level of complications arise when Georgia's wannabe boyfriend, pianist Oscar Farrar, follows Georgia on board. And a third level of complications arise when Elvira and Michael individually decide to be in Rio when the ship docks to find out first hand what's going on. Uncle Lazlo seems to be around for all the proceedings and seems to know everything that is transpiring, but he just doesn't know what secrets to keep and which to divulge.