Cena vs Rusev's rematch at WM31 is going to happen with WWE continuing the feud this past raw. A Match stipulation will most likely happen and the following have been rumored all over the web.

I Quit Match

lumberjack Match

Last Man Standing

Career vs. Championship

Last Man Standing or I Quit will more than likely be reserved for Extreme Rules

It'll be a standard match like he had with Wyatt last year.

If they didn't have One at fastlane I would agree, but they will add something to it to give Rusev a reason to give Cena a rematch. A I quit match would give him the chance to make Cena say I quit, and Career vs Title would give Rusev the chance to end Cena's career. Last man Standing I think will be their rubber match at Extreme Rules, but at WM I bet for an I Quit or Title vs Career. imo standard won't happen.

Career vs Title would be shit IMO. I think it's just gonna be No DQ with the Extreme Rules rematch being I Quit or Last Man Standing

Title vs Career or I quit are the most likely to happen. Because Cena can use the idea of making him say I quit or ending his career to bait Rusev into giving him a rematch.

I could see it being an I Quit match for sure.