Dominion vs TNG Borg, Borg.
Dominion vs Voyager Borg, that's a closer fight.
I think the Borg would eventually win, but it'd take a very long time, and the founders would get away. But they'd probably send only one cube at a time, and they'd probably be able to handle the first cube.
I can imagine, in the long run, the founders just kinda sacrificing all their subjects and most of their Gem'Hadar and just escaping to another galaxy.