Carry on is usually okay unless you have some real high speed film or are making multiple passes through the machine. You can ask for hand inspection. If you are going to do that have the film out of boxes and in something like a clear zip lock bag. Makes things go much faster.
NOT put film in your checked bags. The new scanning machines will turn it to toast. (Every time I have flown recently the TSA
folks have made it a point to ask if I had any film in the bag as it will be ruined.)