7 teams failed to have a defenceman rank in the top 30 (40+ points) for scoring among Dmen this year:
Anaheim, Detroit, Carolina, NYR, Chicago, Edmonton, Vancouver
Note that Washington would be on this list if Carlson walks as a UFA at the end of this season.
Of those 8 teams, I'd say Washington, Carolina, Anaheim, Chicago, and Edmonton could be viable options from Karlsson's POV.
Things to consider:
Carolina may see Hanifin as a 1D soon
Washington may re-sign Carlson
Anaheim doesn't really need an upgrade on D, but they do lack a "true 1D"
Chicago had a bad year, so Duncan Keith could rebound
Edmonton is the one team that can absolutely use EK, but the asking price will be super high
As for cap... any team can afford EK if they want to. The assets they give up is what is more important.