From the LA Times blog Show Tracker:
They may not be able to sing in the Macy's Thanksgiving Day Parade on NBC, but the cast of Fox's "Glee" will get to strut their stuff during the World Series.
Fox has confirmed that cast members from its new hit musical comedy "Glee" will sing the national anthem during Game 3 of the World Series, currently scheduled for Oct. 31. That game will be either in Los Angeles or Philadephia, depending on which team ends up in the series against either the Yankees or the Angels.
Actually, according to MLB.com, Game 3 of the World Series is an NL home game, so the Dodgers and Phillies are currently playing for the honor.