I think Cain wins, but I don't think it'll be easy at all, Cain imo has the cardio advantage so he would definitely keep the pressure on Jones for 5 rounds unlike DC. I don't think Cain would be able to get Jones down early, but may be able to later in the fight. Cain will likely get taken down himself, but get back up quickly. I think it would be back and forth early, but Cain will slowly start to wear on Jones.
Also there are certain advantages that Cain has over DC that will allow him to do better, cardio as I've mentioned is a big one, but also KO power, DC has power as well, but aside from KO'ing Big Foot, he hasn't really showed big KO power. Cain on the other hand has, KO'd Big Nog, made Brock break dance, KO'd Big Foot 2x, and first guy to rock and drop JDS 2x and still the only guy to have done it. I don't think Jones would be taking too many of Cain's punches easily.
Another thing I believe (especially after watching DC lose) is that Cain has more heart, I don't think Cain would have stopped like DC did even if he was tired, Cain said it himself after the JDS fights, he was definitely tired, but he didn't let up, he kept pushing until the job was done, with Cain you have to put him out in order to stop him, which is what JDS did in the first fight. Cain really is a terminator that will not stop until his job is done.
It's an interesting fight, tough for both of them I think, but I think Cain takes it via relentless pressure and having overall better tools. I've read people saying that since Jones beat DC, and Cain is basically almost the same, Jones should be able to beat him too, but Cain is different, he is much better imo.