There has been speculation on plans for Braun Strowman at WrestleMania 32. One of the rumored matches for the show is Braun Strowman against The Undertaker. In the latest Wrestling Observer newsletter, Dave Meltzer noted that as of this writing, nothing is locked in for The Undertaker at WrestleMania 32.
If John Cena is able to recover in time then the plan is still for him to face Taker at the show. Based on how fast Cena has been able to come back from previous injuries and the fact that this show is going to be their biggest ever, I would not be shocked if Cena was able to come back in time. If Cena is healed enough from his shoulder injury, then they could just have him appear on Raw for 3 to 4 weeks leading up to WrestleMania and just not have him do anything physical until the match happens.
Braun Strowman is being protected so it looks like they do have long-term plans for him. Whether or not it will be against The Undertaker remains to be seen.