The Black Cats have agreed personal terms with the 20-year-old on a five-year contract, and club-to-club talks are now under way to finalise a transfer that Toulouse value at around €30 million.
Sunderland are understood to have beaten both Newcastle United and Bayer Leverkusen to the France under-21 international's signature, with the opportunity to become a key figure in Régis Le Bris's side cited as a major factor in his decision. Methalie made his senior breakthrough at Toulouse last season, starting 30 matches in Ligue 1 and earning his first call-up to the France under-21 squad in October, and would fill the left-back void left by Léo Cirkin's departure after five seasons at Sunderland.
The move would follow a familiar pattern for Toulouse, whose academy has produced several talents who went on to move to bigger European leagues. Should the transfer be completed near the reported valuation, it would represent a landmark deal for the French club at a time when many Ligue 1 sides are feeling the effects of the division's wider financial difficulties.
Sunderland's pursuit of Methalie comes as Enzo Le Fée continues to establish himself as a key figure in Le Bris's midfield, having scored an exceptional long-range strike in the club's 4-2 pre-season defeat to Liverpool at Geodis Park.
Reflecting on his display, Le Fée said he was benefiting from a settled role through the centre of the pitch.
"Since the end of last season, I've been playing in the same position so I think it helps me a lot to always be in the same position. I like to be in the middle, have the ball and control the tempo. I want to be one of the best players in this position but I have to work even more than I already do," he said.
Le Fée also praised his side's response in difficult conditions in Tennessee, with his goal followed by a Timur Tutierov strike in the second half.
"It was tough because it was really hot but I think it was really important to play in this temperature because when we go back, it'll be easier. I think we did well and it was a really good first half. Even the second half, the young players did good things as well and scored a really good goal so we keep going for pre-season," he said.