Auto body repair & detailing: Sealer/primer, spray cans, primer surfacer

Question
what's the best sealer to use when using a lot of filler and whats the difference between surfacer ,primer ,sealer ?

Answer
A primer surfacer can be built up so you can block sand any imperfections. A primer sealer is just a thin coat to cover any bare metal or paint edges that you do not want to bleed through. Most brands will do the job. Spray cans are not the way to go