Mtl gives up a 3rd so Seattle takes Byron instead of Allen.
Kulak can either be packaged in this or traded to another team who needs a depth dman.

Byron only has 2 years left so he's not a long term burden. He brings speed, leadership and great value on the pk.

Drouin will most likely request a trade and getting a dman back would make the most sense.

Could be Dumba, could be Ristolainen in Buffalo, could be Graves or Dunn through Seattle if either ends up being one of their expansion picks.

The wild could use help on the wings to complete Kaprizov, Fiala and Greenway (Parize and Zuccarello are slowing down quite fast). Buffalo needs everything, so does Seattle so these are probably the most interesting options as far as trade partners goes.

Ideally, you'd want a dman to play the right side though as Weber and Petry aren't getting any younger. The left side already has Romanov and Guhle as likely locks for the top 4 along with Norlinder, Harris and Struble as options to complete the left side. The right side doesn't have much aside from Fleury and he's most likely a 3rd line pairing.

Getting younger on the right side is a need. Weber is most likely gone after next year. His salary goes from 6m$ to 3m and, then, 1m, 1m and 1m$. He'll either retire or will become a hot commodity for a team that wants to artificially boost its cap (like Arizona) or a team who's rebuilding and doesn't care about the cap hit but looks for vet leadership to show the kids the way (like Buffalo).

Trading him to use the cap space to get an upgrade who brings more of what Bergevin has brought over the last year: sandpaper and has won the cup.

Coleman could be an option. Saad would also be high on that list. Both would be upgrades.