Canon has written something about their new upcoming EOS-1D X Mark II on the page of websites that the sensor which is expected to be planted in this camera will be of 25 mp is being tested in the testing centre. But however it’s rumor so nothing more to be serious about it.
Here what Canon rumors actually writes:
We’re told that the sensor currently being tested in the EOS-1D X Mark II is 25mp. The sensor will be manufactured by Canon, so any third party manufacturing rumors can be quashed before they start.
This source is also confirming the likelihood of a new pair of DIGIC processors to handle the added resolution and maintain the frame rate of the current EOS-1D X.