As for why I would choose Radcliffe to play him: the guy is essentially a magician, card tricks and all, and magic was once his specialty.
He was once portrayed admirably by Taylor Kitsch in the otherwise reviled X-Men Origins: Wolverine before being recast with Channing Tatum in a film that did not survive development hell, but with X-Men now in the hands of Marvel Studios after the Disney/Fox Merger, maybe he can finally be given the best of both worlds.
While he is at it, in case Kraven the Hunter does not pan out for whatever reason, maybe Daniel Radcliffe should also look into trying on a Cajun accent because I actually think he might be even better suited to fill the role of Gambit – a bio-kinetic mutant who has previously fallen victim to some bad timing.