'Speed' Actor Joe Morton on Board for 3rd Film, if Vehicle is Right

Joe Morton would love to reunite with Sandra Bullock and Keanu Reeves for a 3rd "Speed" movie ... but isn't yet sold on the plot, TMZ has learned. The actor tells TMZ ... he'd love to be a part of "Speed 3," after Sandra and Keanu both expressed an interest in rebooting the franchise. However, Joe -- who played Lieutenant Herb 'Mac' McMahon in the OG -- says there are some big questions that need to be answered…