Bonus Characters:
Go to Mayhem mode and highlight Set Teams. Press and release Circle + Square. Now press Select (4x), Start (3x), Square(2x), Circle, Circle + Square.

Bonus maps:
Go to Mayhem mode and highlight Accept Teams. Press and release Circle + Square. Now press Select (4x), Start (3x), Square(2x), Circle, Circle + Square.

Map select:
Go to Strategy mode and highlight Set War. Press and release Circle + Square. Now press Select (4x), Start (3x), Square(2x), Circle, Circle + Square.

Thanks to Revolution readers TimmyBoo and Mikael Luttinen!