I'm guessing Ottawa would want more than they traded Duchene for (from us): 1st + Makar/Girard + Bowers ++
I'd rather gamble on Karlsson hitting free agency next year. Apparently the Karlssons really liked Ottawa so I could see Colorado be an appealing destination. If the Avalanche improve on last year somehow, they'd have as good a chance as any team in the league.
Ideally, Karlsson gets traded to Las Vegas unsigned because I don't think he'd stay there. Las Vegas is about as different from Ottawa as a city can get.