This is a fun little exercise for the imagination!
Truth to tell, I once for fun worked out a reimagining of DS of my own, complete with casting suggestions! I fell back on the entire DS canon, picking and choosing as I went (drawing upon 1840s Gabriel for certain elements with Roger, for instance). Part of this was casting Ellen Page as Daphne, Roger's autistic daughter (replacing David)!
Well, we know Johnny Depp is Barnabas. And the odds are pretty great that Helena Bonham Carter will be used, but given her age and general attractiveness she'd be more my choice for Elizabeth. For one thing, she just did the whole "unrequited love" thing with Depp in Sweeney Todd and methinks she'd rather do something else.
If he is still alive--and my own hope is that he will be--Christopher Lee is a fairly obvious choice for Joshua Collins, presumably in flashback. Again, he's something of a Burton regular.
An actress I'd like to see used is Rachel Hurd Wood, who was so memorable in Peter Pan and Perfume: The Story of a Murderer. IMHO she's hasn't really had that many chances to show her acting chops, but what she has done shows real ability. And she knows her way around a costume drama! But maybe for that reason I'd rather she play either Vicki, Carolyn or (maybe) Angelique.
Frankly, Angelique should be black. Given the back story, one has to wonder while Josette would have a white maid. Frankly, Gina Torres of Serenity fame would be my first choice. Or Rosario Dawson.
Along those same lines, I would rather like to see Summer Gau as Josette or maybe Carolyn. Apart from being beautiful and talented, she has this strange, almost fragile quality. For those of you who don't know her, Summer Gau starred in both Serenity and in The Sarah Connor Chronicles. Then again, depending on how Burton goes with things, she might also make a wonderfully eerie Angelique.
The single biggest improvement, IMHO, between the original DS and the 1991 remake was the casting of Joanna Going as Victoria Winters. She was simply superb, not least because she came across as someone with a brain and a backbone. That is precisely the direction methinks Burton should take with that character. She is, after all, supposed to be a teacher and that really does require some toughness as well as people skills. As you can probably tell by now, I'm a fan of Joss Whedon so my hope to see Amber Benson from Buffy as Victoria should shock no one (she also played a "good vampire" on Supernatural). Not that she's the only choice by any means! Since I'm trying to restrict my choices to actors who are not superstars (lest the whole thing become an overblown epic) other choices for Vicky that come to mind include Zoey Deschanel, Elizabeth Harnois and Eliza Dushku.
I'm not at all sure Julia Hoffman belongs in a feature film of DS. Seems to me the story of Barnabas has rather a lot of romantic triangles in which he is one of the points--Josette/Angelique, Maggie/Vicky, Julia/Vicky, Carolyn/Vicky, etc. Needs some kind of trimming to fit into two hours. Given that, Dr. Hoffman is certainly a viable character to remain--especially if either Maggie or Vicky are dropped. But methinks Julia works best as someone to whom Barnabas is not attracted. But that comes back to who ends up cast as Josette et al, because that shows what his tastes might be. Given that--and the evident scientific accomplishments of Julia--I would suggest a woman not quite as attractive and/or rather formidable in her own right. MIchelle Forbes (BSG and Kalifornia) comes to mind, as does Lori Petty (Tank Girl). Or Molly Parker because she can play ANYTHING.
Different people see Roger Collins different ways. At heart we have a younger brother in a wealthy family, eclipsed by his sister and something of a failure in his personal life. Is he an alcoholic or just a hard drinker? A cold, hard man or a merely a weak one? Whatever those choices, he almost certainly needs to be in his forties or so, or at least come across that way. William Peterson is leaving CSI. John Heard might be available. Although he kinda violates my "no superstar" rule, methink Ben Affleck would make a very interesting younger brother to Elizabeth.
Mind you, if there is another STAR a la Johnny Depp in the film, it would most likely be his love interest--be that person Maggie, Victoria, Josette, Carolyn or some combination therein. So here are some fun possibilities, none of whom have worked with Depp before as far as I know...
Scarlett Johanson
Keira Knightly
Jessica Alba (who seems to want to stretch herself as an actress)
Reese Witherspoon
Anne Hathaway