Whyte better stop. He was worn down by heavy fighting (against Chisora in particular) and Povetkin stole his soul. I'm sure he knows that and he shunned Wallin for it.
Wallin by KO. He'd be better on the inside and big enough to handle Whyte. Doesn't mind dirty fighting as well.
Do not read too much to the last Wallin fight. Wallin just turned up after abandoned his training months before when Whyte pulled out. It was just a spar more than serious form fight. No one really sure how good Wallin is. I think other fighters avoiding him because he might make them look bad. Not worth a risk for them: if they win it's not enough credit. Wallin = still a bit unknown quantity.
However bad Whyte may have looked against Fury, Wallin looked worse in his last fight. I think he’s just not very good.