James, I've seen it go either way. We have never let Lola get to the point where she is in labor...we have scheduled both of her c-sections in advance. I don't think that I could, in good conscience, let her get to a point where the c-section would be considered an emergency. I am a planner, so I would rather know when the puppies are coming rather than have to wait around and worry.

We schedule our c-sections at 61 days, just in case momma decides she wants the puppies to come early!
On the other hand, the breeder we got Dora from allows her Bulldogs to free-whelp unless it is obvious their labor is not progressing (bitch is tired, not pushing, no pups born after 2 hours of active labor, etc.). She has been breeding for 20 years, so she is pretty well-versed in Bulldog labor. Dora's mom actually free-whelped both of her litters prior to Dora's litter, and there were 10 puppies in each of those litters!
As far as our Pug goes, it is pretty evident when she is in labor. She starts digging and rooting around, then comes the panting, then she gets the "glazed-eye" look where she just stares and pants. It is fairly obvious when she starts having contractions because you can see her back arch and her back-end muscles tighten (signifies a contraction). We usually have to help pull the puppies out because of their head size. For her first litter, it took 5 hours for her to have 3 puppies (the middle puppy was really big and got stuck, so we had to pull him out); her second litter took 2 hours for her to deliver 5 puppies (she was a champ with that litter); and her third litter took 7 hours to have 4 puppies (she had a hard time). We are currently expecting her final litter and we are going to go ahead and have a c-section done and get her spayed while she is iunder--no more puppies for her!
Hope this helps!