Let me play the other side here. Is it justifiable for the Canadiens to part with a key asset to get Dubois at a cheaper AAV than it will cost in 2024? There are two RFA years remaining and the ability to sign an eight-year contract. In 2024, it's all UFA years that cost more and a seven-year maximum which would still run a year later than signing Dubois now. The optimal time to give Dubois a contract is this summer when you get a little bit of cap relief relative to open-market value and a better chance at ensuring you're getting him in his peak years.
I'm also not sold that the Habs will have a boatload of cap space in 2024. Yes, Drouin, Dadonov, Allen, Byron, Edmundson, and Hoffman will be up. But not all of those players are going to replaced by rookies on entry-level deals either. Caufield's raise will take up the savings from Hoffman and Allen if he gets a deal that's closer to Suzuki's and chances are that a veteran or two are going to be signed to replace some of the outgoing players. There isn't a big spending spree on the horizon for a couple of years from now and at that point, they might be planning ahead towards replacing Price with a new starter. There might be room for Dubois at that time depending on the contract demands but if someone like Dvorak or Anderson (if not both - some believe both are in Montreal's current offer with the third element being the holdup) are traded for Dubois now, it's a longer-term salary offset that makes it easier to afford him plus you get him a bit cheaper on the cap.
Is it worth parting with some assets to get Dubois the most optimal long-term contract? There's a case to be made for either side.