Ah the information did not come first to Cantor. Who else Cantor told aside from the FBI director has yet to be reported. My wild guess is that Boehner is the one that put the lid on the information. Personally I would not have minded if it all were kept quiet until Petraeus showed up to testify and a House Republican asked Petraeus on live tv, "When did President Obama know about your affair"?
Who knows what scandal the Democrats may have had on an important Republican that they would have let out if the General’s scandal were aired before the election.
Many years ago I was doing political volunteer work and an insider told me that one candidate’s son had an illegitimate child, while there was something equally damaging about the other candidate. It was agreed to keep mouth’s shut by both sides.
Maybe that's it. Maybe it was Ubanga/Holder who dispatched the "whistle-blower" to the Republicans in order to short-circuit such a scenario.