This is a very simple exploit to do.
1. Enter the cheat: TRGTEXC.
2. Enter Maters Countdown clean up as Mcqueen.
3. Pause and go to switch event.
4. Choose Mini-Games and choose Sheriff’s Hot Pursuit.
5. You should have Lightning Mcqueen.
Source
I did this once, but the other way around, with McQueen a Speeder in Single-Player.