Gustafsson in no way gives you the same level of play as Barrie. Barrie is average to below average defensively. Gustafsson is abysmal.
None of those guys you listed are appreciably better than Barrie or Vatanen and some would cost assets to acquire. I don't see how Dunn, Gustafsson, Ghost, Weegar or Stecher magically improve the defense if Barrie or Vatanen don't.
In any event, I'd bet anything that Barrie signs in Vancouver so cross that one off the list most likely.
I'll just disagree with you guys on Barrie. Aside from 2018-19 where he was alright or the closest to average he's ever been (and probably why Toronto banked on him staying alright), he is generally an abysmal defensive D-man. The value from Barrie is PP and in the offensive zone, but if he's not with a rock, huge liability. I am actively cheering on the Canucks to pay for him knowing they don't have the rock to play him with either. Ian Cole in 2018-19 was massive for Barrie, Cole is so underrated.
Our PP was 1st in the league. We didn't lose to Chicago because we didn't have guys getting points. It was because Nurse, Bear, Klef, Russell were so bad in our own zone, our forwards defensive positioning was garbage and the goaltending wasn't elite enough (Koskinen was fine, lots wasn't his fault) to cover the mistakes.
Tyson Barrie doesn't fix that.
Weegar is a better defensive guy, him and Ekblad together were pretty solid, I didn't quite read a post on Weegar/Ekblad earlier but from watching the pairing he held his own well. Stecher is up and down but not a huge liability and it wouldn't cost much. Gustafsson isn't great defensively but to me it's comparable to Barrie. I do agree that I don't think we have trade assets potentially to get in on some of the younger fits.
I don't mind Vatanen but he's a concussion away from missing half the season and retiring.