Probably depends on how impressive the respective wins are. If one of them wins a close fight, whereas the other gets a stoppage in the first round, then it's probably going to go to the guy that won via stoppage. Leon also has the advantage of fighting the bigger star in Nate. If he beats Nate decisively (which he should) that will draw more casuals to Leon's future bouts, and so the UFC will probably look to making Usman vs Leon, since it could end up being the bigger fight for them.
It's hard to deny either guy a title shot, the both deserve one. Colby does too. But Colby kinda messed up by not taking a fight, and now unless one of these guys drops out of a fight, he's stuck being the odd man out. I think in an ideal world, we'd have gotten Usman vs Colby II, and Leon vs Wonderboy, then the winners fight. If Masvidal still wanted to be in the WW picture, then he should have fought Burns. But somehow we've ended up with this really stupid, far from ideal scenario where Masvidal has been granted one of the least deserved title shots ever, perhaps maybe the least deserved in WW history. Colby only wants Masvidal or Usman, so refuses all other match-ups, basically putting himself on the sidelines. Then with the guys we do have left, they've gone and matched them up terribly again. Leon Edwards should not be fighting Nate Diaz. Wonderboy vs Burns kinda makes sense I guess, but Leon vs Wonderboy would have been way better.
If Leon beats Nate, it really doesn't mean anything at all. It'll mean a lot of casuals and maybe the UFC, since it will have more eyes on Leon. But as far as actually beating top ranked WWs, it is entirely irrelevant. It's not something that should warrant a title shot.
WW is a stacked division, and it's also in a really weird place where so many guys have cases to fight for the belt. It's almost impossible to deny Colby, Wonderboy, or Leon a title shot at this point. And after another win, Burns will be back in that category too.