If Rollins beats Cena using every dirty trick in the book, he'll still look ten times better than he would if he beats Kane clean. At least Cena is a big star. If Rollins is put against Kane, it's going to look like his match is just a filler match, despite being the champion.
It's bad enough that Lesnar vs Undertaker was immediately announced as the main event, completely overlooking the actual champion. If they made it obvious that Rollins' match was filler by throwing him in against a guy as lacking in credibility as Kane and he'd look like a chump. Like they didn't consider him to be a star at all.
I'd much rather see him against Cena.