The pair have been friends since the age of 12, when both were starting out in the youth ranks at Middlesbrough.
"It's funny - everyone seems to go their own way in football and move round clubs, so it's great to be playing alongside him again," Cattermole told safc.com.
"Johnno is a great talent, always has been. He has that ability to go past players and our fans will really like him.
"I'm sure he'll do great with us and I think he'll find a lot more space and grass in front of him than he was used to at Man City.
"Adam will love the challenge of playing here and is from the area too. I spoke to him [about the move] and told him he will love it at Sunderland.
"He's a great lad too and will fit in no problem. I'm sure we'll see that in his performances."