Federation wins without even firing a shot.
You have Sisko living in the Celestial Temple and you bet your life them Prophets are watching both sides of their wormhole. So when the Dominion decides to launch their invasion and send how many tens of thousands of ships (with millions of Jem'Hadar), Sisko will see this and he'll get his Prophet buddies to wipe out every Dominion ship that enters the wormhole.
The Dominion will quickly get the message and they'll skulk around in the Gamma Quadrant. So hundreds if not thousands of Dominion ships lost and not one life lost in the Alpha Quadrant.
Of course the real rematch is if the Dominion decides to expand in the direction of the Alpha Quadrant, but that could taken dozens if not hundreds of years conquering all of that territory plus integrating it into the Dominion so that the supply lines don't become stretched.
So when the Dominion does arrive in the Alpha Quadrant the Federation would have plenty of time to prepare. Besides given the numerous deep space missions, the Federation is bound to receive early warning of the Dominion's expansion, plus given Voyager's return and all of that futuristic technology. The Federation may just have a chance and hold out...