Ideally, we trade Marner and a depth guy (Aube-Kubel, Aston-Reese, Engvall, Holl) for a legit top 6 guy that isn't old and isn't an upcoming UFA, a "just okay" depth guy that makes too much money but is an upcoming UFA (this is to make the deal work with the cap), and a REALLY good prospect or 1st rounder, and maybe even another half-decent prospect or 2nd rounder).
If we traded him in the offseason, more teams would be interested and we MIGHT get more in the trade.
New Jersey, NY Islanders, Nashville, St Louis are probably interested. There are other teams that I imagine might be interested if we are willing to take a player back in the trade that they HAVE to include to make it work... Buffalo (Jeff Skinner), Philadelphia (James van Riemsdyk), Winnipeg (Blake Wheeler), Los Angeles (Iafallo and Walker), Vancouver (Tyler Myers and/or one of Boeser Garland).