The 18-year-old Le Havre defender is expected to head for England to complete his switch with the two clubs having agreed a deal some time ago.
Left-back Mendy has also been linked with Arsenal, Lyon and Marseille this summer, but the player has indicated that the Stadium of Light will be his destination and Press Association Sport understands the transfer could be completed within days.
That would represent a major boost for manager Paolo Di Canio and his recruitment team, headed by new director of football Roberto De Fanti.
The Black Cats confirmed three new signings on Monday as defenders Valentin Roberge and Modibo Diakite and midfielder Cabral officially became Sunderland players after running down their contracts at Maritimo, Lazio and Basle respectively.
But work is continuing apace to further re-shape not only the first team, but the development squad too. Di Canio is hot on the trail of Velez Sarsfield's 21-year-old right-back Gino Peruzzi, while Le Havre midfielder El-Hadji Ba, 20, is expected to complete a Bosman free transfer sooner rather than later.
The Black Cats are also close to adding Arsenal goalkeeper Vito Manonne to the ranks after agreeing a fee with the Gunners over the weekend. Italian Mannone, 25, made 13 appearances for Arsene Wenger's men last season, although his last game came in November after number one Wojciech Szczesny had returned from an ankle injury.
He spent the remainder of the season on the bench with Lukasz Fabianski getting the nod when Szczesny succumbed to injury once again in March.
A move to Sunderland may give him a better chance of competing for a first-team place, although he would arrive with Keiren Westwood seemingly the man in possession following Simon Mignolet's departure. Liverpool paid an initial £9million for the Belgian, representing a significant profit on the £2mil the Black Cats had handed over three years earlier.
Di Canio is desperate to recruit at least one striker, and AZ Alkmaar's United States international Jozy Altidore has been heavily linked with the club. But there could be further departures too amid speculation that full-back Phil Bardsley, skipper Lee Cattermole and playmaker Stephane Sessegnon may leave.