This is like the Leafs Kerfoot packages.
Why would the Canucks consider this?

You get a top 4 D-man on a very cheap contract. A 25-year-old 2nd/3rd Line player and a 1st Round pick in a deep draft. Why wouldn't they consider it?

Mayfield is a UFA at the end of the year and will likely get at least what Gudbranson got if not more, and he’s probably too old for the Canucks core. The Canucks are also loaded at winger, so they have no need for Beauvillier. The 1st is nice, but nothing else fits the Canucks needs

You get an elite top line C/W on a cheap contract. Beau is a 3rd liner we have plenty of.
A good but older UFA RHD. The pick is likely a mid 1st. If a top 10 Lou is a goner.

Starting a package without Dobson but $ in $ out probably needs 4 pieces coming back one being a dump.

To be honest, I think trade talks between the Isles and Canucks might have happened at/near the Draft. Now I don't think so much. Canucks were probably interested in the 13th pick. And now the Islanders don't really have the assets to swing it/not the assets Canucks would want.