You didn't mention when you'll be travelling, but music at The Gellions tends to start later (about 9:30 p.m.), so you could check out what's happening at Hootenanny, and if it's not to your liking, you could pop around the corner to The Gellions.
You also didn't specify if by trad music you meant instrumentals, songs, or a combination of the two. If you meant the singing tradition, then if Davy Holt or Caman (Davy with Stuart MacKintosh) are at the Gellions, you'll be in for a good night. Davy does a lot of trad and contemporary songs, and has a wide knowledge of Scottish music. He takes requests, so don't be afraid to ask!
If Schiehallion are performing, you'll be in for a wild night. They have at least one piper in the band. The above mentioned Stuart MacKintosh performs with Schiehallion as well. One of their "Big" numbers is "Scotland Forever," which was written by the much maligned Tommy Scott. I think their version is somewhere on YouTube.
You might want to check out Living Tradition magazine www.livingtradition.co.uk as you get closer to your holiday. They're fairly dormant right now, due to the virus, but they have listings of concerts and sessions throughout Scotland on the website. You could also check the listings of folk clubs in Scotland to find out if there are any concerts or sessions you can attend on your way south. You should also be able to catch a session or two at Sandy Bell's in Edinburgh.
Good luck, and enjoy the music!