Get a preseason under his belt and give him a clean slate for next season.
Best thing Cannon can do is get some sort of partnership with the likes of O'Hare, Hamer, Brewster etc (if Brewster stays) over the season, which should make him play better.
Look how Campbell plays with the above 3 mentioned players, they don't even have to look where Campbell wants the ball, they just know, and vice versa.
Take O'Hare's goal against Bristol City in 2nd leg, he knew exactly where Campbell was going to put that ball, and timed his run accordingly, same with Hamer's ball to Campbell in the final, they've got that mental connection which is what Cannon needs to form with them.
On paper, Campbell and Cannon should be an ideal partnership, on their day, they're both capable of creating and scoring goals at this level.