Ya just knew Canelo Alvarez and Gennady Golovkin were not about to walk away from MILLIONS ... finally hammering out a deal to set up boxing's long-anticipated rematch ... this according to Oscar De La Hoya.

Despite the fact the two sides were at loggerheads for months, ODLH tweeted out moments ago that a deal has been made and the fight is set for Sept. 15!

Oscar had previously set a noon deadline for GGG to accept his final offer, but c'mon ... with that much money on the line, everyone on the planet knew the deadline wasn't REALLY a deadline.

Noon came and went ... and finally at 2 PM, the deal was announced.

Oscar's problem was the GGG's camp wanted a 50/50 revenue share -- and Oscar said that was WAY too much money.

Unclear what the final deal entails.

The rematch was originally slated for Cinco de Mayo, but it was derailed when Canelo tested positive twice for PED. As we reported ... Canelo started training again, only this time he knows his next opponent. The fight's set to happen at T-Mobile Arena in Vegas.