I think Sandra Bullock would be great as the Baker's Wife if she didn't have to sing. Sandy can't sing. She's said so many, many times. She would never take the part even if it were offered to her.
I'm guessing they will go with whoever is the "hottest" at the moment who can sing and is somewhat (at least) right for the role. I would look for "star turns" in the Witch, and even perhaps the Narrator. The Baker would probably be a film name, but not necessarily a mega-star. Assuming it's a name, I would love to see someone like John Cusack or Robert Downey Jr.
I also hope they don't cast the Baker and his wife too young, meaning early 20s. I would rather see late-30s, to 40s even if the Baker is supposedly Rapunzel's brother. But if they take that info to heart, look for younger leads ... like Jennifer Lawrence and Jake Gyllenhaal. Or ... the other Gyllenhaal (Maggie, who has the perfect look for the Baker's Wife, IMO) and James Franco.
As far as the Witch, I'm still in the Zeta-Jones camp. I think she has the perfect combination of beauty, eccentricity, talent, and a dangerous edge to her work as a film actress. She's my #1 pick.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22