Marleau is not getting traded. He has a no move and why would he want to be moved if this team is a favourite to win it all. He signed for the leafs to have a crack at winning the cup.

Unfortunately English isn't my native language (even not second), but OK, I'll try to explain it in poor English. Next summer Marleau will get his 3M signing bonus and then his cap hit will go to someone who has problems with Lower Limit, for example to Ottawa (without EK65 and Ryan) or Arizona, ect., where he immediately go to retire. As a result TML has 6,25M Cap Space; Arizona has couple of picks and 6,25M Cap Hit (retirement isn't give a cap hit relief because of 35+ contract); Marleau has 3M money. Or if Arizona will have salary arbitration, they will get second buyout window and can bought out final year of his contract. Arizona has 6,25M Cap Hit (because of 35+ contract); Marleau becomes UFA and can sign 1-year 1M contract with SJ.
Or if you think that it's impossible, OK let it be like this: Upper Limit 83M; Zaitsev to NYI for draft-picks; Nylander to Preds for Subban; Marleau stays in Toronto. Or if Upper Limit 80M, instead P.K. let it be Josi, or Ellis, or Giordano, ect. There are might be thousand ways.
Sorry if my English was too bad.