dude u have to thing this is u job now u have to make it work. that what paid u for dude. so if u have to have win what do u do?
It's an unrealistic request but OK. The only reasonable time for it to happen would be Money In The Bank since it's the only PPV before Summerslam. The logic would be as follows:
-Have Ryback or Cena say to the other that after Payback, this thing between the two of them is over. After all, how further can you take a feud after a Three Stages Of Hell match? You can't get a better sense of finality than that.
-Cena retains, and the next night, he gives a promo at the end of the show while holding up the WWE Title that he and the WWE Universe can overcome any obstacle or opponent that is put in front of them, and now Ryback knows this just like all the others. Out comes Paul Heyman, who says that if Cena is really looking for a new challenge, look no further because he has the perfect challenge for him. Cena laughs, saying that Curtis Axel has gotten two count out victories over him due to interference from Ryback and so now he must think he deserves a title shot? But Heyman says no. He states Curtis Axel will be WWE Champion one day but the man he is talking about is Brock Lesnar. He says that since Lesnar has run through the COO of the company twice (the second time being inside a steel cage), he thinks he should be next in line for a title shot. Cena says that if Lesnar wants a shot, he'll have to tell him himself face to face next week on Raw. Cena then says he has another message he wants sent to Brock, and preceeds to lift up Heyman into the AA and then drop him.
-Lesnar shows up the next week and from here on, it's pretty standard build. I could come up with stuff for the next three Raws but I can't be arsed when the general set up for the title match is pretty much already laid out. Cena accepts, Heyman says that Lesnar as WWE Champion is "money in the bank" (to tie the PPV name into the feud), Cena admits that he was intimidated by Lesnar over a year ago when they first squared off but that's because the loss to The Rock had him down. Since then, he's defeated The Rock, regained the WWE Title, survived a brand new monster like Ryback and so he's not so intimidated this time.
-Lesnar wins the title at MITB on July 14th, 2013. From there on, do whatever.