It's probably between Liljegren or Andreas Johnsson for the Leafs. People already thought Dermott and Kapanen were strong players last year.
Johnsson is a bit of a older prospect but he had some troubles coming to N.A. He got laid out with a dirty hit and concussed in first game? in the AHL. To end last year, him and Kapanen were easily the best forwards on the Marlies to end the year and into the playoffs. And it's carried on into this year.
He's one of the biggest sleeper prospects on the Leafs to me. He does everything well and some things very good->great. The only caveat is he's a bit of a older prospect so it's difficult to gauge his upside, there's definitely a chance he busts out altogether secondary to a lack of potential for growth. I've been calling him one of the biggest sleeper prospects for a while, he's looked better than Kapanen to start the year (Kapanen might have better tools but Johnsson is just as dynamic but uses his toolbox more + has better general instincts). He reminds me of a poor man's Ehlers/Guentzel with his playstyle.
With Liljegren, he had a horrid draft year secondary to mono and bouncing around on a terrible SHL team. What he's done this year so far at least, sort of reaffirms the talent he's always shown.