i have rplaced all my handles even the rear trunk. unscrew and pop open the inside or facial cover. unscrew the handle from the inside and pop handle off. put new one in....body shop will charge 100+ so just buy the part at a parts store using your friends discount card.. It will take 10 min to complete repair.
The sliding side door are a little problematic. Toyota have several Technical Service Bulletins describing door handle replacement and adjustments for the door. A company called Alldata supply information that most independent repair shops use and allow car owners to get access to information most of which is straight out of the Toyota manual. If you do some work on your Sienna you will like this site.A year subscription is inexpensive and you will have component location, wiring diagrams, torque specifications and lots more. http://www.alldatadiy.com/