Despite what Travis Yost wrote on TSN, a Karlsson to Tampa trade doesn't make sense for either side.
Ottawa would want something like Sergachev/Point + Palat/Johnson + 1st/Foote/Howden, and rightfully so.
But Tampa is already arguably the top team in the league and doesn't need to make that big of an acquisition, or give up that much, to push them over the top.
If Karlsson's traded, he'll be traded to a good but not great team that thinks he'll vaunt them into the top tier (like Anaheim, LA or Dallas). If he ends up in Tampa Bay, it'll be because he signed there as a UFA.