United fly 744, 777 and 763ER metal on international overwater routes.
The 777s and 763s have seatback PTVs throughout Y, and both have 18" seat width in both E and E+. The 744s have 17" wide Y seats and only ancient wall-projector movies, no PTVs.
If your ticket is booked in fare classes Y, B, M, E or U you get E+ seating at booking (assuming it's available). On any lower Economy ticket class you can try for it at check-in for a fee - don't know what that's currently running for TATL flights - or if you'll be flying more than a few times you can buy a full year's access to Economy Plus for USD299. Anyone with Star Alliance Gold or Silver status on another *A airline (e.g. BD, LH, etc.) also gets E+ for free.