For those that have been through the training or know people who have, what do most find is the most difficult or demanding portion of the training ? Is it the physical training at FLETC, learning spanish in a short period of time, or the flight training at the air training center ? Is there a certain percentage who don't make it through or is that rare ?

The idea of flying for CBP and protecting the US is of great interest to me, but I have no idea what to compare something like this to since I have never attended military or law enforcement training.

Maybe consider the military? Invaluable experience and you make lifelong friends and contacts. I'm guessing you're fairly young so it would definitely give you some seasoning that IMHO all those going into law enforcement should have. I personally think LE should have a bare minimum age of 25 as life experience goes a long way toward relating to some of the individuals you will encounter. That said your aviation experience would valuable to the military as well. Good luck.

Do majors take CBP pilots??

This will be an interesting question from the current/past CBP pilots who have been around awhile.
the ones I know who moved onto airlines all had a military flying background, so they didn’t get the major job off of the CBP experience only. MY GUESS is that someone who has no other experience than CBP were not hired directly into the Major airlines.

Of course... we hire experienced pilots from all sources. Need to have multi time of course...

It never ceases to amaze me how many BUBBAS come out of the woodwork crawling to CBP when the airlines take a crap! Look, the job is for you to be a LEO who happens to fly. You will have a BADGE on your chest. You will carry a FIREARM. Flight time is NOT rapidly gained here. If your dream is to fly a 787 10 days a month for 300k a year don't come here!!
If you want to log a lot of time go fly 121 and move up. Period! CBP is a serious career not a place to step on. Bottom line, you will be flying something that directly supports someone on the ground who eventually puts cuffs on bad guys! Many love it here and many hate it but for the most part almost all remain at CBP until retirement. The velvet handcuffs are tough to break.
Flame away.

^^^^THIS^^^ I flew with a retired CBP pilot a few years ago On the 767/757... he was hired into a commuter for a year/two after retirement then jumped to United when we started ramping up hiring again after the merger. He had some pretty good stories and he enjoyed his time with CBP... and the check every month. He was probably In the late 40’s/early 50s back then.

The LE academy is not that difficult. Not a big deal for someone who has been through all the training involved in being a pilot. If you have enough brain power and judgement to be a professional pilot, it is highly unlikely you couldn't make it through FLETC. Not making it through FLETC is rare and usually is a result of integrity issues, not the difficulty of the course.

Flight training within the agency is typical of what you have already been through. A vendor course for the aircraft you are flying (like Flight Safety) and then an in-house syllabus in the actual aircraft.

This. AMO is the career you never thought of when you got into aviation. But is absolutely a career position and should be approached as such. We do have aircraft that will get you to a major airline, but if you start here without previous twin turbine PIC, it will take a whole career to accumulate the hours.

An exception might be ugleeual's type: that experience level will bring value here even just for a few years. But I would expect AMO to be wary of those types. But, who knows.

One point I differ with RCpilot on: In my view (and experience) we are pilots who happen to be LEOs, not vice versa. With few exceptions, our job is to fly and leverage that skill set to enhance the ground mission. Like most flying jobs, we are really paid to bring back the aircraft with all the paint and all the people. No AMO pilot has ever been written up for not putting cuffs on enough bad guys, but plenty have for unsafe flying. JMHO.

Like I said above: You will be flying an A/C supporting someone on the ground who will eventually put cuffs on bad guys. Too many want to come to CBP and just build time for their next job.
Some have shown up not even realizing carrying a weapon was part of the job! Was a branch guy for years supporting most of the 3 letter alphabet gov/ state/ city types. Now enjoying the view from the mighty Orion! Stay tight and fly safely!