The Toronto Maple Leafs cannot trade forward Mitch Marner unless he agrees to waive his no-movement clause (NMC).
Marner, who is under contract for one more season with a $10.9 million salary cap hit, controls his fate. There is no indication from within the Toronto Maple Leafs organization that suggests a desire to trade Marner, but that hasn't stopped the speculation and trade rumors. (All salary cap info from capfriendly.com)
The Leafs could present Mitch Marner with a few favored destinations and see if he'd be willing to go to those teams before asking him to waive his NMC. As much as Marner will tell anyone who asks that he loves playing for the Leafs, I'm sure there are a few other teams he wouldn't mind playing for.
However, even if the Leafs can convince Marner to waive his NMC, any possible trade is unlikely to happen before July 1st. Due to the structure of Marner's contract, he is due a $7.25 million signing bonus on July 1st that most teams would like to avoid paying. After the signing bonus, Marner's base salary is $775,000. This means that even though he would count as $10.9 million against a team's salary cap, the team only needs to pay him $775,000.
Some teams in the NHL have internal budgets, and these budgets can prevent them from spending the maximum salary cap amount. Having Marner on your team for a $775,000 salary while helping you eat up cap space with his $10.9 million cap hit is an attractive business opportunity. It is unclear how much Marner will seek on his next deal, but one would think a contract extension must be part of any trade for him to agree to it. Here is a look at a few possible trade options.
Clearly the Leafs are in a weak position if they trade Marner, so it's at least plausible they could wait until paying out the bonus in order to maximize their return.