Anyone know a way to do this? Is there a Cydia app or a certain file I can crab using file on the iPhone and transfer it to the iPad mail app?

Use a mail provider that supports exchange sync, such as gmail or hotmail. Setup the account as exchange on both devices, they then will sync over the air.

For gmail instructions are here: http://www.google.com/mobile/sync/

If I understand what you are asking correctly, then no, you cannot sync the passwords of your mail accounts between devices. If you change your email account(s) password you must change it on both (all) devices that you own AFAIK.