One Borg Cube will be stopped, provided the Star Wars forces deal with it quickly and decisively.
We never saw the Federation deploying the huge fleets against a Cube that they deployed in Deep Space Nine to fight the Dominion. The first battle was 40 ships (many of them old models, some even dating back to the time of Kirk) vs. a single Cube, and the Cube annihilated it. The second battle I believe had a slightly smaller (but more modern and powerful) Federation fleet fighting a single Cube again, and once again the Cube wrought havoc, but tellingly the Defiant was able to survive and do damage.
I don't think there's reason to think that the fleet that attacked Cardassia, or the one that retook Deep Space Nine, both of which numbered in the thousands, would have been destroyed by a single cube.
Similarly, the Imperial fleet at full strength comprised what, 50,000 ships twice as big as Galaxy-class ships on average? A single cube isn't beating that. The sheer energy output of that amount of firepower would probably turn the cube into a giant plasma globule.
...However, if the cube is allowed to run amok and assimilate lots of ships then things might get a lot dicier (no pun intended--and possibly no pun made)
The Borg win here..
once they view the Star Wars U as a thread a few drones will die but than they will adapt, after they adapt The Star Wars U becomes one with the Borg
Data said it best..