According to TSN's Pierre LeBrun, Marner and his agents aren't putting together a no-trade list, nor do they have any plans to move on from the Leafs before his contract is over, something not a lot of people saw coming.
https://x.com/theathleticnhl/status/1797978127039377883?s=46
As I wrote a few weeks ago, the Marner camp, led by agent Darren Ferris isn't putting together a list of teams for a potential trade. The focus for Marner, who has a full no-move clause, is on honoring the remaining year of his contract and seeing where things go from there.
That also means I don't think there's an appetite to talk extension come July 1. The preference from the Marner camp is to start the season and see how things go. Perhaps there are talks on an extension eventually, but I don't believe there's a strong desire to get into them this summer.