After a lot of trying this and that I came down to masking with tape.
First I find it is best not to use tape straight from the roll. The edges are raggy if you look closely where they have been cut in the factory. I find it best to place a piece on a cutting board and with a Morton blade cut a sharp line through the tape. I then have a sharp tape edge which helps to stop paint creep under the tape.
Use a new American razor blade (the ones with the thick metal backing one side) to cut the ends of the tape on the plastic canopy. This blade has a finer edge than the Morton. Bed down the tape edge with a blunt instrument. Some use toothpicks I use a small rounded end clay model detailer wich gives a good clean edge.
Been using the Vallejo matt varnish as a primer to one seal the tape edges and two provide a matt base for the paint. Using primer I find you get an edge in primer colour and also primer tends to be thicker than paint. Next time I am going to try a thin coat of Humbrol Clear as a primer and edge sealer.
I find it is best to
airbrush as you get a thin fine coat with great coverage. With hand brushing a thicker build up of paint I find hinders a good release on the tape removal. However careful with hand brushing I get thin bits and need to give another coat giving an unwanted build up.
After curing, just, so that it is still a little soft I use the American razor to carefully score between the tape and paint. Then with huge foreboding and much stress I remove the tape. As mentioned before toothpick any excess which after the scoring with the blade should still give a clean line. Where I may have been unlucky I use a fine brush with Vallejo
Model Air slightly thinned and a magnifier to carry out a make good job.
A lot of bother but for me the first thing you look at on an aircraft model is the canopy.
Laurie