Unlock: Use Trevor, Complete Minor Turbulence
Requirements:
Champion: Finish first without using shortcuts.
Head to Paleto Bay. The swimming part is fairly easy, just keep going at a normal rate. For the biking segment, go max speed when you reach the flat grounds. Accelerate when approaching the stunt jump to make it. For the final part, just keep running normally, or hit your gas tank hard if are behind the race.