It's a fact that Grams (Storm) warned Bishop that "the Askani son" would protect Hope as an infant. It's very likely that Cable knew Bishop would be the one to try to kill her. It's also known that Cable contracted out when he asked that giant RETCON, spoilers:
end of spoilers, to help during Messiah Complex.
Do you think Cable sent Sage on a mission to neutralize Bishop?
Sage, Bishop, Cable & Hope all like Big Guns
Cable and Sage rejoined the X-Men together. In fact, Cable's attempt to protect Senator Kelly was the mission that drew Tessa back into the fold. Hungry for future knowledge for vague and shadowy reasons, Tessa sought out the Destiny Diaries. It's likely that she was also drawn to Cable and Bishop for their information.
As a member of the 06, Cable knew Sage could be trusted.
As the most competent of the original X-Men, Cable knew not only could Sage be trusted to go undercover, she would go the extra mile and sell her body to accomplish the mission.
Sage seduces Bishop's rival [via jealousy]
Sage mesmerized Bishop. She dressed to the nines. She played him. She seduced his rival to bait his jealousy. She played the fop. She played the victim. She played the leader.
Sage tricks Bishop into chivalry.
Have Sage, Cable and Deadpool been partners all along? Should Sage run X-Force?
Sage wants the Professor and Bishop to listen to reason.