I wouldn't take Williamson in the ODI team. That leaves Franklin at 5, hopefully not needing to bowl (Nicol can be your 6th bowler if needed). Agree with B McCullum at 6, I think he is still the best ODI closer we have, but also agree that he will in all likelihood open.
Edit: just looked at Williamson's stats on cricinfo and they are actually a LOT better than I thought they were. So having said that, I would play him, (which is back to leaving Franky out again!

), but he has to bat at three. I don't like him down at 5 or 6 as he really does need time to build an innings, so if we are going well and we get to 35-40 overs 3 down, do we really want him coming out to bat.
Kane averages 61 in domestic od's, so yes, I agree with your edit :). Definitely not a 6-7 batsman though, definitely has to build his innings.
I find it interesting we've put him in the t20 team, must be as a specialist bowler