Another great pairing could be John Wick and Blake. Blake has her own issues with a dark past and being on the run, similar to John Wick in some ways. They could bond over their shared experiences and John could help Blake in her fight against the White Fang. They would also have some great combat scenes together.
John Wick and Qrow could also be an interesting pair. Qrow is a skilled fighter and has a bit of a rough - around - the - edges personality. He and John Wick could compare their combat styles and experiences. They could also team up to take on some of the more dangerous Grimm or other threats in the RWBY world.
John Wick and Ruby would be an interesting pairing. Ruby is young and full of energy and hope, while John Wick is a jaded and highly skilled assassin. Their interactions could be really cool, with Ruby learning some more hardcore combat moves from John and John learning about the power of friendship and hope from Ruby.