The Borg win
Jem'Hadar will be adapted to with ease, Vorta again no problem, as soon as the dominion weapons are adapted to they haven't got much of a chance, the dominion would be worn down, they'd last a while but they'd be worn down.
The Founders are a different story, can the borg assimilate them? if not they sure can kill them, or glass the founders planet.
So yes I do think the Borg will win.
And I know the Dominion have a large territory and a lot of ships, so do the Borg, Borg space was made up of "thousands of star systems" and the borg were about 3 minutes away from destroying earth with ONE cube. Their entire millitary might is nigh on unplayable
Dominion are outgunned here in a straight up war.