I am blasting my car trailer and noticed that after blasting there seems to be a White film left. Is this film going to cause a problem if I just spray my primer and paint over it or does it need to be removed?
I would think that any film on the bare metal is going to cause you problems. Paint jobs are only as good as the foundation and if you go through the trouble of blasting to strip everything down, why not do a wash with lacquer thinner and a metal prep before priming. You don't want to have to worry about paint lifting months or years later after going through all that trouble just to have to do it all over again because of shortcuts early on.
The white film may be galvinization. If it is very hard to get off, but it sands off or comes off with a wirewheel with some effort, it probably is. IF that's what it is, it is a good rust preventative and should be left alone. Just prime with a good primer after washing it down good with thinner.
It could be that the trailer was galvanized or possibly aluminized before it was painted. This would account for that white film. To find out you could take a small area and see if blasting on it more will go through and turn the metal to a silverly color.