Fathers' Day (1997)

Smart-aleck lawyer gets a visit one day from an ex-girlfriend who tells him that her son is his. Enter writer Dale Putley, a depressed goofball who meets with the same ex-girlfriend who tells him her son is his. One day Jack and Dale meet and discover that they've been told the same story by the same woman. Which one of them is her son's actual father? And where is that son? He is following around a rock band called Sugar Ray, so Jack and Dale hit the road to Sacrament and find "their" son--drunk and lovestruck. They take him to their hotel room, but he escapes and they must team up to find him again, get him home, and find out which of them is his father.