This is an absurd proposal.
McDavid is not going anywhere.
If he were going to the Leafs -- which he is not -- Matthews would have to go the other way. Neither team does that.
I actually don't agree with it having to be Matthews. It legitimately wouldn't even make sense for the Oilers to go after Matthews because its safe to assume Matthews would walk as a UFA from the Oilers sans McDavid. If the Oilers are trading McDavid - they're blowing it the hell up for multiple years.
McDavid won't get traded unless he absolutely demands it and things get ugly. If he did, other teams would be a much better fit than Toronto - so it would require him demanding to go to Toronto.
A world where McDavid demands to go to the Leafs would require obscene dominoes where the Leafs trade Marner to someone else (or the Oilers if they wanted him, but again for similar reasons to Matthews I expect they wouldn't) and then its just a ridiculous amount of picks, prospects, and RFA team controlled young options.
So yeah, not happening.