Replacement: No one. But Zac Efron if we really must press ourselves.
"Street" Smarts: Zac has that uber-pretty (yet potentially rebellious) quality that made Johnny break out of this joint to become what he is today. Just take your chances, Hollywood, on a squeaky-clean Disney star, and he might just surprise you with how much range he has.
*Disclaimer: Before the hate rains down, let me simply say no one can ever compare to Johnny. But duty calls, so we must choose a mini-Johnny*