The idea that Matthews, Tavares, Nylander or Marner's contracts are a problem for the Leafs is flawed. The Leafs will have some contract issues, and might even have to trade someone they don't want to, but it's not likely to be one of those 4, and those contracts are not an issue.
The $11.95M the Leafs have committed next year to Marleau, Kessel and Zaitsev is far more of an issue. If you manage your cap well, none of those other contracts are even a mild concern. Even if you get to the point where you have to trade someone, if you are doing it while having no wasted cap space, it's not a difficult problem that has you trading away your top players.
The reality is the Leafs may lose some future value to move a contract they don't want to, or may lose out on some players they would likely rather keep (Kapanen or Johnsson), but moving Marner won't be the solution unless someone offers something completely silly.