Weegar and Manson aren't upgrades worth giving a ton for. If people want to upgrade the RD than it's going to take a bigger trade. The 1 for 1 type of trade like Mitch Marner for Ryan Ellis or Mitch Marner + for Aaron Ekblad type of trade.
I like Marner a lot but his salary is prohibitive given the Leafs already have Tavares and Matthews making what they make. The Leafs should move Marner and take that money and spread it out a little better imo.
Moving Marner could be tough because of his salary but not because he isn't a great player. I think Dallas would be a good trade partner if they'd move Klingberg. Something like Klingberg and Pavelski for Marner. The money is almost the same and addresses issues for both teams. More pieces could always be involved however.