The boring answer is, probably, what they are on now/riding in the world cups. Expect they will be one or two swaps from big to small/small to big but most will just ride what they are used to. Much better to ride a bike that’s familiar to you then change last minute hoping to find a small advantage.
I think it’s safe to say that it’s the best rider(s) on the day will win regardless of wheel size.
A pretty boring answer I know!
As to which wheel size suits the course best that’s a different matter but again I suspect there’s little in it really.