Apple uses Fed Ex as their sole shipper.
Daily our Apple warranty parts are shipped the day prior and arrive early morning, then later after noon a Fed Ex employee picks up replacement parts we have to go back to Apple. It's an ongoing daily routine Monday through Friday(we are closed saturdays) and picks up Monday where Friday left off.
So I think it's safe to assume and also being that Fed Ex is about the only Saturday shipping service in the U.S., that it would be Fed Ex to ship the iPad's on the 3rd.
On the other hand if demand is so high for pre orders, I could see them moving over to also including USPS and or UPS.