All three players will arrive at the Stadium of Light on free transfers at the start of July.
Sunderland boss Paolo Di Canio is keen to reshape his squad after narrowly avoiding relegation from the Premier League last season and he has moved quickly to agree deals for Roberge, Cabral and Diakite.
Roberge has been plying his trade with Maritimo in Portual, while midfielder Cabral has also just ended his contract with Basel.
A number of clubs have been linked with Lazio defender Diakite, but Sunderland have won the race for the central defender.
The signings have been made on advice of the club's new director of football Roberto De Fanti and chief scout Valentino Angeloni.