It's an interesting and fair question, personally I would prefer if they became friends, and I don't like how they made her evil and killed her in DSITMOM, but Sora could probably win, Scarlet Witch is powerful, but Sora has fought a Witch (some would say fairy) before, he or any keyblade wielder could probably take her down, but again Wanda (I'm just going to use her name from now on because I don't feel like calling her two words at once) could also win because she took down a bunch of wizards, the only one who fared better was the Sorcerer Supreme,(not Wong, I like Wong, he's one of my favorite characters, but he's no Sorcerer Supreme, I'm hoping strange takes the tittle back at some point), it's really up in the air, Wanda could win or Sora could win, another factor could be that I don't think Maleficent is as powerful as Wanda, like I said it's really up in the air, it also depends on hypothetically why there fighting, like for example is Sora trying to help the people at kamataj (I'm a really bad speller) or is he helping doctor strange as they travel through the multiverse, also another factor I just realize, she could influence the things around Sora thankfully Sora doesn't have a voice that can harm himself by taking his mouth, or a friend with a bigger mouth that spouts his weakness to someone with reality shaping powers, wow this is hard I don't know who could win.