The official Tekken website was updated recently detailing how the pre-order bonuses will work for the game. If you pre-order at select retailers you'll get early access to DLC characters Kunimitsu, Ogre, Michelle and Angel. GameStop will give you all four DLC characters while if you pre-order through Amazon.com or Best Buy you'll only receive early access to Angel and Michelle.
Keep in mind that even if you choose not to pre-order the game, the DLC characters are free you'll just have access to them at a later date. Tekken producer Katsuhiro Harada mentioned via Twitter that you will never have to pay for additional characters.