There's nothing obvious about those matchups.
The franky one is a concept you created because you think it fits. I would rather go for the fact that San Juan is called "battleship" and Franky's poster is now a picture of the sunny, a ship.
Devon's fight is against either Nami or Robin. nothing obvious about which of them is gonna be. You could argue about Nami usually fighting chicks, but Lafitte is also a possibility for her due to both being in the same position of the crew (navigators).