The 24-year-old midfielder moved to the Welsh side at the start of last season and despite making 29 Premier League appearances, found himself out of favour towards the end of the campaign.
The former Celtic man is confident Sunderland manager Paolo Di Canio can help to revive his fortunes.
"He (Di Canio) has done interviews about me which gives me a lot of confidence and also when I was a kid, I saw him playing so I’m really looking forward to working with the great manager in this team," he told the club's official website.
"I did well I think last season, we won the cup (League Cup), and then we did well in the league but I want to play some games, I want to show my quality to people but I did not get my chance this year.
"So I had to move to the club who really need me, need my quality.
"There's always pressure for the new boys but I have to overcome that and I have to show why I am here, that is the main thing I have to do."
