Wow. That's a good one.
I'll admit that I'm on the fence for this one.
I think it depends on your definition of the Force.
If you view the Force as a 'spiritual' sort of energy that connects all living beings, then I believe the entire Collective would gain the appropriate knowledge and training to wield it.
If you go by the more modern definition of the Midi-chlorians within the Jedi's body, then I would have to assume that only that individual Borg would gain the ability. Or, that Borg, and any others within the collective that also had, and would be capable of manipulating, midi-chlorians if they had jedi training.
It's also possible that they might lose the ability to use the Force altogether, in the assimilation process. Either by cutting off their link to the Force as a spiritual energy, or by destroying the midi-chlorians within them.