JVJ really has to have the high notes -- he's practically in falsetto in "Bring him Home." I just can't picture anyone other than Colm Wilkinson; Hugh Jackman has the acting down, but his voice isn't up to the role in my opinion. I can't picture Ramin Karimloo because he's too young, and too slight, physically.
I saw Samantha Hill in, I think, her second performance in Phantom. She was the alternate Christine, for all of a few weeks, until she moved past Marni Raab to be the main Christine. She is incredible, and would be perfect as either Cosette or Eponine.
I've been spoiled by the 10th anniversary concert--I decided that Alun Armstrong, the relatively unknown British actor who also plays serious roles, is one of the best we'll ever see as Thenardier. However, I think Nathan Lane could give him a run for his money. As for Mme. Thenardier, she needn't have a brilliant voice, but she's got to have comic timing. For some perverse reason, I'd love to see Madonna in the role.
I think Aaron Tveit would make a good Marius -- someone of his talent is wasted as Enjolras.
That leaves Fantine and Javert. I can't think of anyone for Fantine, except Sierra Boggess. My rule on Javert since the movie came out is "ABC -- Anybody but Crowe." I think Javert should be a baritone, to contrast with JVJ's tenor. I can't remember Mandy Patinkin's vocal range, but I think he looks perfect for the part and could pull it off as an actor.
You alone can make my song take flight.