I don't see the Leafs trading Matthews but if the contract talks don't go well this summer, maybe. Difficult situation and nobody knows what is on the mind of Matthews. I think he stays but the Leafs are going to have to pay him big time. 8x $13M-$15M range.
If he is traded, that's a massive contract to move in a season where it's still a flat cap. No doubt teams will line up to make offers but there would be salary going the other way more likely. And then I wonder if that team wants permission to talk extension before the trade is official. Trading Matthews is easier said than done... especially with a mindset of getting the return value you want.