I doubt it was a complete "publicity stunt" because they wouldn't spend that much time and money searching all of the US, going to England and Australia just to pre-promote the movie.
I believe they were and possibly still are searching for an unknown. And say if Shannon or someone else from Broadway gets the role, its because they didnt find what they were looking for in the open calls and/or the studio wanted someone who could handle the job.
"Zac is sweet as can be. He's very much just a sweet kid from California who happens to have a face that looks like it was drawn by Michelangelo, (if Michelangelo did anime)."
-Adam Shankman.
"I haven't left this building since Windows 3.1!"
"Celebrating a birthday this week: Rene Descartes is 412! Do you know who he is? Then why are you watching this show? You could probably get into college and even get one of those job things. As for the rest of us; Amanda Bynes is 22! Yay!"
-E!'s "The Soup"