WWE reportedly wants to have a bout between Brock Lesnar and Cain Velasquez at some point. Reports state that WWE has had meetings with Velasquez and further reports state that the reason WWE had Lesnar destroy Mysterio and his son on Raw last night was part of setting up that match. If that's true, then it seems like talks between the two parties are going quite well. The idea, or part of the idea according to what's been reported, is that Velasquez takes exception to Lesnar's attack on Mysterio and his son, due in part to Mysterio's iconic stature in Mexico and Velasquez's Mexican heritage so take it for what it's worth at this point.
WWE would almost certainly bill this as a clash of titans type of situation. Velasquez is someone who stacks up well against Lesnar: he's about 6'2", generally weighs anywhere from 245 to 265 lbs., has a respectable MMA record of 14-3, is a two time UFC Heavyweight Champion and a decorated collegiate wrestler including being a two time NCAA Division I All American in 2005 and 2006.
Velasquez has stated that he'd be open to working with WWE or AEW, which translates into whomever is willing to give him the most money, and, again, IF WWE set the angle up with Lesnar and Mysterio last night as part of a plan to build Lesnar vs. Velasquez, then his talks with WWE must be going really smoothly. Of course, if things go south, WWE can always say it was simply Lesnar being Lesnar, going on a rampage, doing what he wants, etc..