There would be no reason for French dialects. The movie will be in English. One doesn't go to see The Three Sisters with an American, British or Australian cast and expect to see it performed in a Russian dialect. Unless one is in Italy, one doesn't hear productions of Romeo and Juliet and The Merchant of Venice performed in an Italian dialect. It is safe to say that unless one is in Germany, Doctor Faustus is not performed with German accents (one would hope!(.
As to what specific dialect in the English language is used, it will most likely be standard UK English (just because conventionally, for better and often for worse, classics are typically done that way), but it could just as legitimately be American. An argument could be made for Australian given the leads are both Australian, but I doubt that the production would do that, not only because Les Miserables with Australian accents would seem quite bizarre to its target audience, but because it would be ridiculous to expect an entire supporting cast of non-Australians to master the dialect when two Australians already more than adept at English and American dialects are playing the lead.
One would expect that the cast would use the same national dialect, with parallel sub categorical distinctions (conveying "class," regional differences, if need be), to convey that they are compatriots. While the characters are French compatriots speaking French, the actors are not speaking French, but English, which is why it would be quite silly and unnecessary for all of them to affect French accents. (of course this would be different if the film had made a decision (which would have seemed to say the least bizarre) to primarily cast French actors, which it did not).
Updated On: 3/21/12 at 11:48 PM