I don't see this happening. Rock in any title program at Mania doesn't make any sense to me. Rock vs HHH? The title has no purpose being in this feud. Rock vs Reigns? You'd just get Reigns booed out of the building and expose him on the mic in the worst way possible. Rock vs Bryan? Bryan might be the only person that wouldn't get booed against The Rock but even then, this match is a pipe dream. Rock vs Lesnar? Forget about it.
However, if they were to do a non-title Rock/Lesnar program, the Rumble could be used as a convenient way of jump-starting it. Have both guys enter the match, have Rock eliminate Lesnar, and then have Brock lose his shit and take Rock out of the match and put him through a table or something. Things escalate from there and they meet at Wrestlemania. However, that doesn't seem likely given Brock is a babyface now and this feud in itself doesn't seem like it will probably ever happen. Just an idea, though.