I think it will be more. $6.5 - 7+, but it will depend on term.
If you look at similar defencemen who signed for 6 year deals after their ELC the same year that Trouba did his 2 year @ $3M bridge deal:
Lindholm 6 years @ $5M
Ristolainen 6 years @ $5.4M
Jones 6 years @ $5.4M
4 years @ $6.5M would bring him about "even" in total dollars had he signed a similar deal to those guys. So I think that is the minimum. If you want to sign him for more term, price will go up.
Trouba's points totals against those guys was down last year, but he was hurt a bunch. All top pairing guys on their team.
Then again Chevy pulled off some magic signing Scheifele and Ehlers to the contracts they are on, so if he can get Trouba long term @ $6M, I would be ecstatic.