The Ulsterman and his players returned to work with O'Neill having completed the first part of his mission during the second half of last season by easing the Black Cats clear of the relegation battle.
He will now seek to fulfil owner and chairman
He told the Northern Echo: "This season is Martin's main season. He has had time to prepare for the summer, I'm sure he will bring some more players in.
"He will really want to stamp his authority on the side and it's a really exciting year. Hopefully it will go well - I'm sure it will."
O'Neill is currently in the process of re-shaping his squad, although former Aston Villa defender
He has been linked with a series of potential targets, among them Blackburn Rovers duo
But he is delighted with his capture of 30-year-old Cuellar, and Cattermole too is hoping there will be more to come.
He said: "Carlos has been a great player over the years in the Premier League. It will be good to have him on board. It shows what Martin thinks of him to sign him again.
"It's a great time of the year, when you get new faces and there's a fresh approach to everything. Everyone is fresh. We are all just looking forward to the new season."
Professional Footballers' Association chief executive Gordon Taylor has confirmed the union has been contacted by Sunderland players about manager Paolo Di Canio and that it is investigating the recent fines issued by the Italian.