The Borg would ultimately win. They have a huge number of large, nearly invulnerable cubes.
All that Voyager junk aside, no ordinary military power has figured out how to beat one cube easily, let alone a fleet of them.
as for the Founders, based on TNG, if the Borg can't assimilate it, they will eradicate it, or claim it is obsolete like they did Data.
They would either wipe out the Founders, or capture one and try to find out how they work. They could easily find out their home world by assimilating the right Vorta.
On the other hand, since the crew of Voyager knows how to infiltrate the Borg, avoid being assimilated, steal technology from them, face down their queen, and destroy an entire Borg complex, anything is possible.