Ideally, you and your wife are on strong footing in your marriage and communicate well, both verbally and non-verbally. You're 'gonna have to let her know what's on your mind before you go to the resort, especially if she wants to purchase some new swimwear, lingerie, and club outfits. If she agrees at some point that it might be fun to have a "threesome" with a sexy guy, she'll need time to shop. All that said, there's one key element without which it will never happen. You need her "buy-in." Not necessarily to go the full "cuckold wife" route like you read so much about in this forum, but rather, - she needs to feel secure in your marriage and know that she can play a bit (flirt, go commando, engage in touching with other guys, etc.) without any threat to your marriage. This will all be a surprise to her and sometimes "surprises" go south.
Have a glass or two of wine or a couple of drinks, and talk with her about a "dream" you had. Not a dream about unrealistic cuckolding, bbcs, gangbangs, her humiliating you, huge penises in her anus, and so on. Rather, a dream about her and a sexy guy dancing at the bar, maybe going back to your room for a nightcap, kissing, touching, clothes coming off and a sexy threesome just sort of happening with you in a passive role as they made love. Then describe how erect you were watching her kiss him on the dance floor, and later having an orgasm with him, etc. etc., and let your wife articulate her views of what could happen, what she sometimes thinks about. Midway through a discussion of your "dream," you'll know which way the wind is blowing. And you may not get any more feedback for weeks. What will you say if she asks you: "didn't that make you jealous?" or "if I like the guy I might want him again".....
Even then, she may not be up for it. You'll just have to live vicariously through the rest of us in here. And finally, it's my view that once a husband plants the seed of a mfm threesome, the topic will come back up at some time or other. If you are smart, you will let her be the one to bring it up, and put it into play or totally hate it.