Couture was drafted 9th overall in 2007 and was an integral part of the Sharks' consistency under former GM Doug Wilson. Couture would provide any team that acquires him a very solid second-line center that can perform in the playoffs. In 116 playoff games he has 101 points and has scored clutch, timely goals throughout his playoff career.
If the Sharks are willing to retain some salary, Couture could be an excellent fit in Toronto. Even if the Sharks were willing to retain $2M-$3M per season, having a player like Couture in the fold for the next 5 seasons would undoubtedly solidify the top-6 and give the Leafs several more kicks at the can without having to worry about Timo Meier and his $10M qualifying offer. As far as where Couture might play, he did spend some time as a winger at the start of his career and is a left shot, so he would comfortably slide in at 2LW and could even play on the top line if the Leafs were looking to create a bit of a cascading effect, dropping Bunting to 2LW and Jarnkrok to 3LW.
The Sharks captain does have a modified no-trade clause in his contract, allowing him to submit a list of 3 teams he'd be willing to accept a trade to, but I'm sure the Guelph, ON native could be convinced to come home and challenge for a Stanley Cup on home soil.
It will be interesting to see the potential return the Sharks would get should they and Couture decide to part ways. Of course, the return will be more if San Jose is willing to retain part of his $8M salary each season for the last 5 years of his deal.