The Witch: (so many possibilities, so I'll go in alphabetical order) Marion Cotillard, Penelope Cruz, Nicole Kidman, Michelle Pfieffer, Meryl Streep, Catherine Zeta-Jones (four of these actors have a history with Rob Marshall)
The Baker: John C. Reilly or Eric Stonestreet
The Baker's Wife: Amy Adams (I think it is a given that her performance at the Delacorte is an audition for the film and she has a history with Disney)
Cinderella: Anne Hathaway, Amanda Seyfried or Taylor Swift
Cinderella's Prince: Justin Timberlake (don't laugh, he can sing, he can act, and he has the requisite sex appeal for the part)
Wolf: CGI with JT voice-overs
Red: Abigail Breslin
Jack: Nolan Gold (he'd be perfect and ABC would probably work around his Modern Family schedule since this is a Disney film)
Jack's Mother: Helena Bonham Carter (I would have put her on the list for the Witch but after playing Bellatrix Lestrange the role of the Witch might be too similar)
Rapunzel's Prince: Alexander Skarsgard
The Giant: Melissa McCarthy (a combination of CGI and live action)
Rachel Weisz The Baker's Wife Toni Collette The Witch Josh Radnor The Baker Ellen Page Little Red Lauren Ambrose or Evan Rachel Wood Cinderella Patrick Wilson Wolf/Cinderella's Prince Matt Bomer or Lee Pace Rapunzel's Prince Chris Colfer Jack Imelda Staunton Jack's Mother Christopher Walken Mystery Man
Yes, Taylor Swift. Don't be snob. She can sing (without a doubt) and she can act, if you doubt that look for her SNL appearances and her guest role on CSI.
10 years ago most people would have said Justin Timberlake will never be a good actor. He proved them wrong. He'll never be a Daniel Day Lewis or a Robert DeNiro but he is good at what he does.
Bakers wife- Elizabeth Banks Baker- Josh Radnor Cinderella- Ann Hathaway or Anneliese Van Der Pol The Witch- Michelle Pfeiffer but i wouldn't say no to Nicole Kidman, Fergie, Madonna or Gaga(if they worked with them on the acting and singing and they had gone through the requisite auditions.) Jack's mom: Meryl streep.
I would be extremely upset if they decided to give every role to a Hollywood star. I feel like a show like this could be extremely successful without having a ton of stars in it. The story is marketable enough by itself and if they casted maybe one or two "stars" it could be a very successful film. Also, if Taylor Swift is even considered for the film I will be furious.
The thing is though that it's a musical and people usually try to avoid them. They could think the story was trying to be like shrek, or the fact that woods deals with too many adult themes for it to be a kids movie. And the fairy tale element could repulse the older crowd it's geared towards.
Based on your list, bobs3, I shall respectfully request that you give up trying to understand this beautiful musical and go back to writing Disney Channel / Modern Family crossover fan-fiction.