Did Montesquieu and Voltaire share the same opinion about government?

No. Voltaire did propose a separation of church and state, but did not go into the question how the State should then be organized

• other than advocating a 'fair' judicial system and criticizing

the existing French judicial system. Montesquieu proposed an at the time totally new concept of organization of Government, in which the Church simply played no part.

You might therefore say that they expressed a shared opinion on the exclusion of the Church in a country's government, but not on the other issues.