Replying to a thread at Shoot For The Edit, Nelson hints that Rosie Huntington-Whiteley is Carly on Transformers 3.
Thread: Every Little Girl Should Be Told That She's Pretty, Even if She's Not.
Nelson: I personally like Carly, I mean, Rosie.
Update: It's no longer a rumor or a hint. Nelson confirmed Rosie's role as Carly.