I feel like unless we're talking about supernatural AI the only answer is A&B

Otherwise the box has no real way of knowing what you would've picked, so it's complete RNG.

If there was a realistic way that it could make that decision i'd choose only B, but otherwise it just doesn't make sense.

edit: I also didn't realize until after I read it that box A always has the million dollars. So there's actually no reason to pick only box B in this scenario. The paradox only makes sense if box A is significantly less than box B. It's supposed to be a gambling problem but A&B is completely safe with the changes made.