Mrs. Winterbourne (1996)

Connie (Ricki Lake), unwed and pregnant, is heading to Boston by train when she meets wealthy newlyweds Hugh (Brendan Fraser) and Patricia (also Lake). The train crashes, and when Connie comes to in the hospital, she is mistaken for Patricia, who died in the crash with Hugh. Opting to play along, Connie gets in even deeper when she meets Hugh's family in Boston and discovers no one had ever met Patricia -- and that Hugh has a handsome twin brother, Bill (also Fraser).