Thor and Wonder Woman swap roles
Thor takes Wonder Woman's place in her movie starting with her arrival in London. Wonder Woman takes Thor's place in The Dark World just before the Dark Elves attack Asgard. All of the supporting characters assist them in similar fashion to help them achieve their goals. Who has an easier time finishing the other's movie?
Both are equipped with their standard armor and equipment. Assume that necessary knowledge needed to further the plot is granted to each person (like Thor knowing how to read Dr. Maru's notebook or Diana knowing that Loki is the go-to guy for hidden portals). But they don't automatically gain the other's complete knowledge, only that which is necessary to keep the plot the same.