Goddamnit, I shouldn't have deleted this Raw off of my DVR. I completely missed this part of it (as well as Bryan joining the Wyatts.)
Anyhow, the only way I could see Lesnar being in the WWE Title match at a Wrestlemania is if he's the one walking in as the champion so that he can drop the belt to someone. This is probably a set up for a match with either Batista or Undertaker (who could be entering into the Rumble himself, possibly as a surprise entrant.) After Lesnar just destroyed "The World's Strongest Man" and after he no doubt will dominant the Rumble participants for awhile, Batista coming in and tossing him out would be a great way of setting up a Battle Of The Goliaths type of match between them. If the Undertaker is the man to do it instead, similar deal. Lesnar has his sights on becoming the WWE Champion and if Taker ruins that for him by eliminating him, then he could set his sights on ending the streak instead (as revenge.)
A distant third choice is Roman Reigns. There's talks of him going babyface before Mania and we all know he'll be the most dominating participant in the match, so is it really that far out of possibility that he is the man to toss Lesnar out, thus setting up a match between them at Mania? Probably, but it's something I'm throwing out there anyways.