Yeah, I think the best way is to wank the AAFC. They were relatively successful in OTL, and even managed better average attendance figures than the NFL. Plus the AAFC champion Browns repeatedly challenged the NFL champs to a game after every year. In OTL, the NFL always refused because they didn't want to lend legitimacy to their rivals. Maybe if you have a more forward looking NFL commissioner who sees the game as a chance to acheive more publicity to pro football (which was still lagging WAY behind baseball in popularity at this point) then a Super Bowl analog could be played in 1948-49. Or alternatively, if there were an overconfident NFL commissioner who sees a game between champions as a way to prove their superiority and crush the upstart AAFC once and for all, then a game could be staged at around the same time period. Either way, if the AAFC proves itself competitive, there would probably be a merger in the early 50s with the NFL taking all of the AAFC teams instead of just a few. So pretty much the NFL-AFL merger two decades ahead of schedule. Also, at this point the NFL was still trying to rip off baseball terms to steal fans, so it would prbably be called the "World Series of Football" or some such nonsense.
As to who would play:
Super Bowl I (1948 season) - Browns v. Eagles (close one, Browns were on the rise, but probably an Eagles victory)
Super Bowl II (1949) - Browns v. Eagles (rematch, probably a Browns victory here)
Super Bowls III-VIII - In OTL the Browns appeared in the NFL championship game in each of these years, winning 3 out of 6. Unless butterflies intervene, that will presumably be the same. Rams and Lions will be their challengers for supremacy, but Cleveland is still seen as the best team of the era overall. In the present we would be referring to Cleveland as "Title Town" rather than Green Bay.