Planetary government

What would happen if we (as a planet) were approached by a group of aliens like the ones in Episode I and asked to join a Galactic Senate? One condition would probably be to form a planetary government. Who would lead this planetary government? Is it possible to have a one-world government? We'd also need to pick a planetary senator.

The United States is obviously the most dominant country, but I'm sure there would be global outcry if both the Senator and the World President were American. Maybe if we had to switch to this form of government tomorrow, Bill Clinton would be World President and U.N. Secretary-General Kofi Annan could be Senator. Or maybe we'd want a worldwide celebrity (George Lucas? ) to be a Senator.