#1 A genuine heavyweight
While Velasquez has shown the athleticism to enable him to work with a wide variety of opponents, there is nothing quite like a match between two heavyweight competitors. As a two-time UFC Heavyweight champion, Cain Velasquez is not only a big man, but he has a reputation that fits his physical stature as well.
Matches with the likes of Chris Jericho and Jon Moxley would be intriguing, as well as having strong box office appeal. The same can is true of Kenny Omega and Cody Rhodes.
Cain Velasquez, though, would also work well with AEW's newer acquisitions, such as Lance Archer and Brodie Lee. Both the men mentioned have an impressive physical stature, and a clash for either with Cain Velasquez would be a remarkable spectacle.
Lastly, there is also a potential feud with Bellator MMA heavyweight Jake Hager, in which Velasquez's prior career can form the basis for a unique rivalry. There would be no shortage of big matches in AEW for Cain Velasquez. Negotiating a deal could be tricky - as Velasquez is unlikely to come cheap - but the move makes a lot of sense for both parties.