Just to add to GM1985's informative post, if you were to take Air Tahiti Nui from Paris via LAX, they do have some level of co-operation with U.S. Immigration and people who are on that flight are filtered through a few specific lanes because they know they are are in transit, however you still have go through immigration even though you are not entering the U.S.

3 hours should be fine if you do the BA/AA flight and then connect, but LAX can be very hit & miss unfortunately!

Pilot37