Assuming they give you the choice, and assuming that choice still has similar effects to what it did in the original, I'm thinking Leon first, and then Claire...I know that's not the "canon" route (or at least it wasn't originally), but Claire encountering Mr. X, who is ruthlessly hunting down Sherry, Terminator style, always just felt more 'apropos' to me, while Leon faces the plot's 'main' boss. I also just feel like there's something about first playing as the Cop who's showing up for what's supposed to be his first day, finding the station decimated and the people who were supposed to be his new partners either dead or mangled, and THEN playing as the 'regular citizen' whose experience is potentially even more horrific, also 'feels' right to me. But either way, they both have great stories, and I think the order will just be more of a fun 'which first?' thing.
What I kind of suspect, being that they have to go so much more in-depth with presentation now, is that you'll be able to choose, but the "zap" system will be gone, replaced by two cemented campaigns which are nevertheless playable in either order--and that they will most closely resemble Leon A, Claire B (in all the trailers, we see Claire confronting Mr. X, etc). I'm also curious to see if they turn Hunk's bit into a full-fledged bit of plot, rather than just a timed 'supa challenge mode'.