The assailants shot randomly at the people as they left the church, the sources said.
It was not immediately clear if the two people killed were Christians, they said.
A Coptic priest at the wedding said he was inside the church when gunfire broke out.
Thomas Daoud Ibrahim said he rushed outside to find a dead man, a dead woman, and "many injured".
Coptic Christians make up 10% of Egypt's 85 million people, and have generally coexisted peacefully with majority Sunni Muslims for centuries, despite bouts of sectarian tension.
But the army's overthrow of elected Islamist President Mohammed Mursi on 3 July has been followed by the worst attacks on churches and Christian properties in years.
The immediate trigger for the attacks was a bloody security crackdown in Cairo on 14 August.