The Toronto Maple Leafs should never consider trading Mitch Marner. This should be self-evident, and it shouldn't have to be said.
The Toronto Maple Leafs signed William Nylander to a fair contract, and when Mitch Marner's time comes up, they've give him a couple million more than Nylander got, which he will fully deserve.
Mitch Marner is the still the Leafs second best player. He's a home-grown home-town superstar, and outside of some lunatics with megaphones on Twitter et al, he's the team's most beloved player since Wendel Clark donned the blue and white.
The Leafs will give him a respectful raise when the time comes and would have to be complete morons to trade him.
The Toronto Maple Leafs Are Not Trading Marner
In the NHL, almost no team has ever traded a player like Marner and won the trade. That alone makes it an extremely high risk move.
Secondly, the most commonly mentioned reason to trade him is that the Leafs can't have so many players making so much money. It doesn't matter how many time this extremely uninformed opinion is proven wrong, it pops back up.
Can the Leafs have 4 highly paid superstars? Obviously, they can. They proved this was the correct way to use the salary cap when, during the Covid Pandemic, the cap froze and the Leafs, who, like everyone else in the industry, had expected it to skyrocket because of a new TV Deal, Gambling and Expansion.
The Leafs entire play of signing the Big Four was based on that happening. The fact that it didn't happen and the Leafs remained a top team the entire time proves their strategy is correct. Furthermore, entering last year's playoffs they were able to add an incredible contingent of players (Ryan O'Reilly, Noah Acciari, Sam Lafferty, Luke Schenn, Erik Gustafsson) despite their salary committments.
Those additions made them a heavy cup favorite and the best team in the NHL. Certainly the deepest. That the Leafs never won a cup the last five years was kind of a fluke. They easily could have.
Also, look around the league. Many other teams - Colorado, Florida, and Tampa spring to mind - are copying their startegy (though those teams do get unfair tax advantages that let them have lower cap hits and pay their players more).
The Leafs need to spend the money they allot to non-stars much smarter than Brad Treliving did last summer. The Leafs need to be better at developing prospects.
But what they don't need to do is trade Mitch Marner. Not for anything, not ever. They need to pay him what he deserves - which is basically whatever he wants - and call it a day.
Rest assured, unless the Leafs are the most poorly run franchise in the NHL, they will never trade Marner because the idea of trading him is so stupid. The day he's eligible to sign an extension, they will sign him.