I would say hard no to the Leafs portion of the deal from a Canucks point of view. Its likely to be at best a 22nd or so overall pick and a bottom pairing D. Plus, if they do improve their D, which Tanev would do, they are going to be a hell of a force in the playoffs and it could (hold your breath) be a 31st overall pick. Terrible value for one of the league's best defensive defensemen, who is signed to an ideal contract for a contending team with a lot of big salary commitments. A comparable deal can be had at the deadline, 2020 offseason, or 2020 deadline.
The Lucic portion, I doubt would happen, and that's a lot of money to pay for a 1st round pick from an ownership perspective. I don't see him waiving his no trade clause to come to Vancouver and get ripped by fans and media and hastled everyday on a rebuilding team. His contract also overlaps into a time when the Canucks are hopefully competitive again. I would say if the Canucks are going to look to target a cap dump, a player like Spezza makes more sense as we can absorb the cap hit in the short term, but not the long term.