I'm shocked by the ignorance of this question. Bhuttos are Shias. BB's mother Begum Nusrat is Iranian Shia origin.
Our first President Iskander Mirza was a Shia (descendant of Mir Jafar), Gen. Yahya Khan who was also President was a Qazalbash Shia.
Muhammad Ali Bogra who was PM was a Shia and a descendant of Bengali Nawabs.
Musharraf is a Sunni.
All that said, it is shocking that a Pakistani believes that there is a sectarian bias in our top levels. I'm one of the biggest critics of Zia's sectarian agenda and the Wahhabi/Deobandi mafia that has since tormented Pakistan but Shia-Sunni differences are no factor in our politics.
Considering mullahs bring up and start protesting for the silliest issues (religion on passport) and politicians leave no opportunity to throw mud at each other, is it not surprising at all that Shia-Sunni has never come up in Pakistani politics?