The guy they will likely target via free agency is Bills linebacker Paul Posluszny. Posluszny led the Bills in tackles last season with 103. They also need to either find a linebacker via free agency or hope that someone will step up to play outside linebacker on the opposite side of Michael Boley.
In Buffalo, Poslusnzy is a team leader, not only on the field but in the locker room, and while it would be the Giants gain, it would be a loss for the Bills to lose him. It could come down to where he wants to play more, and if the offer from outside Buffalo is a better one.