News of the World claims the Black Cats are ahead of Aston Villa and Newcastle in the chase for the 23-year-old.
Onuoha signed a new five-year deal with City last year, but has fallen down the pecking order at the club, following the arrival of Roberto Mancini as new manager at the club.
Reports claims Onuoha will be allowed to leave City for just £3million this summer.
