Anytime during Campaign mode go to 'Start New Campaign' at the 'Campaign' menu and choose the character you want to play as. Then return to the 'Campaign' menu and select 'Continue Campaign' and you will start with the character you selected.

If you pause the game and enter L1, L1, Circle, Square ALL the unlockable features in the game will become available options.

This option is enabled when you pause the game and press L1, Up, Down, Up, Left.

If you're struggling with the game and want to unlock this feature you have to pause the game and press Triangle, Triangle, X, X, L2, R2, R1, R2, O, Square.

To unlock ALL the remaining weapons after the primary weapons have been unlocked you have to complete the game on the 'Professional' difficulty setting.

When you have beaten the game on the 'Recruit' difficulty setting ALL the primary weapons in the game will become available options.

This harder difficulty setting becomes unlocked when you have beaten the game once on 'Recruit' or 'Contractor' mode.