To unlock two bonus cars from Subaru and Mitsubishi, you'll need to win the respective championships in the career mode.
Winning the 1.6L series gets you the Mitsubishi Lancer Evolution6. Doing the same in the 2.0L series wins you the 2000 version of Subaru's Impreza WRC.
Winning the 2.0L championship again gives you a 'Level 2' licence, enabling you to get more performance from these cars.