Access all cars in circuit races
To get all the cars you must get a ranking of A in every race.

All cars
Hold L and press X, A(2), Up, Down, Up, Down at the main menu. 

Access all stunt tracks
You must complete each track to unlock subsequent tracks until all of 
them are unlocked. 

Extra options:
Complete all circuit races in first place in each them to unlock extra options at the 
game option menu.

Bonus extras
Finish story mode to unlock concept art, film stills and more.