They could definitely make a showcase from his run to King of the Ring, his brief feud with The Rock, if Hogan is back in WWE's good graces (enough to get back in the game anyway) the brief Hogan/Lesnar feud, his original feud with The Undertaker, the feud with Big Show/Heyman, if he is indeed returning to WWE this year, we could see Kurt Angle pop up in the game this year and the Angle/Lesnar feud could be in there, obviously the Goldberg/Lesnar match is gonna be in there (awful as it may be), he could have his first little feud with Cena in there from '03 I think before they include the stuff from his WWE career post UFC with breaking the streak, Triple H, Cena, etc.
Basically, there's more than enough actual feuds to draw from for a Lesnar showcase.