Most fans pair these two together as they both are well-known place for gambling. (in exception of Las Vegas). With gambling being one of their main-economic sources, they are usually displayed to get along very well.
Most fanfictions portrayed these two as enemies or rivals across the poker table, gambling with chips and a deck of cards and using sly tricks to get the other in a losing position. If this idea isn't the concept of their relationship, they'll be written as partners in gambling.