The Scottish talisman netted 11 goals for the Black Cats after arriving from Wolves last summer before injury ended his campaign in March.
As Fletcher gets set to return from the ankle problem that kept him sidelined for almost half a year, Di Canio says he will place plenty of responsibility on his main striker but insists he will get plenty of help up top.
"I'm happy. I have always said I am happy, but I have to be really happy because he can join the team that can help him to be crucial, like he was," Di Canio said.
"Last year, his goals were very important, but he can be even more crucial and play in some way for his teammates because he has got talent, he has got quality."
As for Fletcher's return, Di Canio hinted that he will be used for the trip to Crystal Palace on Saturday.
"If he is on the bench, he can be involved straight away because he is ready," he added.
"But it doesn't mean he can't start on Saturday straight away. We will see, but anyway he will travel with us because now he is part of the squad and we are happy to have him back."