I agree that whoever wins here will lose in a rematch at Extreme Rules. I could see it going either way - if Cena wins tonight but loses at Extreme Rules, then Wyatt can cut a promo saying that winning the battle doesn't mean anything if you still lose the war. If Wyatt wins tonight but loses next month, then he can simply tell Cena that winning the second battle doesn't mean quite as much as winning the first because people usually only remember the first, and Cena will always have to face the fact that he couldn't get the job done when defeating him would have meant the most (i.e. at Wrestlemania) and that losing the first match, even if you win all the ensuing matches, leaves a certain stain on the soul that is impossible to ever fully cleanse (imagine Wyatt articulating that last part in his usual poetic sort of language.)
Personally, I think it's more likely that Cena is winning tonight. A few reasons why:
1. He's suffered a beat down at the hands of Bray Wyatt the last two PPVs. Something tells me therefore that he may prevail over him in a victory tonight.
2. It's the 30th Wrestlemania. Cena is still their poster boy, they may prefer the idea of him winning over him losing, even though the match with Wyatt isn't main eventing.
3. Something Cena said in an interview on WWE.com a couple of weeks ago may end up being a prelude to the match outcome - he said that he suspects that Wyatt may not even care about winning, but only about hurting his enemies and brainwashing the minds of others. If those words turn out to be prophetic, then it could indicate that Cena wins but then suffers a beat down at the hands of the others and has to be walked/stretchered out of the arena as a result. Wyatt can later spin this in his favor by saying that Cena won but wasn't the last man standing, and for the first time in history, he couldn't walk out of Wrestlemania on his own. If Wyatt then goes over in a rematch at Extreme Rules, then Bray looks all the better for it.