Sunderland secured their biggest win over the bitter rivals in 34 years with a 3-0 victory at St James' Park on Sunday to boost their Premier League survival hopes.
Gardner, who missed the game through suspension, has been impressed by the impact of Di Canio since his replaced Martin O'Neill at the Stadium of Light.
"Obviously when a new manager comes in everybody wants to impress, everybody raises their work-rate and everything really," Gardner told Sky Sports News.
"He has done a log of tactical work on the training field. He's become a legend overnight we have won the derby and the fans love him, the players love him and hopefully we have some good times ahead now."
Gardner watched the game with the Sunderland fans in the away end at St James' Park and the midfielder admits it was a brilliant day for everyone connected with the club.
"Being up there with the fans and singing with the fans soaking up that atmosphere and walking down to the changing room and soaking up that atmosphere I was buzzing from being up with the fans and then you are buzzing when being with the players," added Gardner.
"It was a brilliant day for not only me, but everybody at Sunderland football club."