Horvat is a very good idea. He's a great 2 way player and penalty killer, and always up there in faceoffs. Just checked the numbers, he hasnt been below 50% once his entire career. 53% or better each of the past 4 years. According to capgeek, has 2 years left at 5.5m per. He's not an elite offensive player, but has not exactly been playing on a powerhouse team. He can take some more of the defensive burden off Mika and still probably approach 70 points playing with Panarin.
Would Vancouver want to move him? Petterson is the clear 1 there. They moved our old friend JT Miller to the middle this year and he had a very good year. Maybe they see value in moving Horvat for upgrades elsewhere rather than pushing him down to 3C. He does wear the C for them though, and that's always a question of whether a team will trade their captain barring something out of the ordinary.
If it's not Horvat, we should be targeting someone similar to play 2C with Panarin and Kakko. I still like Lindholm from Calgary and to your point I wouldnt be opposed to taking Lucic along as part of that deal, with some retention by CGY.