UPS (and other flavors of the year, like Fed Ex) have USPS contracts. I believe one of the stipulations to flying the USPS contracts is residence in the US over the last 5 years.

If you go to CX, make sure you are a DEFO on the cargo side. If you go in as a SO you'll go straight to Hong Kong and will possibly de-qual yourself for UPS.

Perhaps someone more familiar (or willing to go read their employment contract) with UPS hireing mins knows more, but I wouldn't set my sights on 'brown' w/o knowing this if I was looking at international carriers.