I recently bumped into a guy at the local hobby shop who'd brought in a finished model airplane. The canopy hadn't turned out entirely to his liking and he asked me, "How do you do your clear parts?"
I smiled. There was no short answer to his question. "I really hate clear parts," I told him. I really do. Over the years and over literally hundreds of model planes, ill-fitting clear parts have caused me more grief than any other modeling problem.
The problem, of course, is that unlike the rest of the model that you can hammer, rasp, shim, chop, or correct with a gob of epoxy putty, clear parts must be pampered and protected. They are styrene in its pure form - very brittle material that is prone to crack if stressed. Squeezing or pulling a canopy to fit a fuselage is asking for big trouble. Building a model to fit its clear parts is a safer practice.