When the Chicago Post first runs the story on Kevin, there is a picture of him on the front page, next to the headline. So anyone who was following the story would have known what he looked like, which would make it impossible for Kevin's friends to get away with pretending to be him.
Part of the movie was shot in Toronto (actually, the guys' apartment is in Toronto, I remember seeing interviews), along with where it takes place, Chicago. If you watch the credits and you watch where the cast is dancing while Al Green's singing, you can see a Tim Horton's Roll Up the Rim billboard in the background. Also, that scene takes place at the Eaton's Centre in Toronto.