Hi Pat,
I use Parafilm M, It's none adhesive and works well. Takes a bit of getting used to though, so if it's your first time masking canopies Tamiya masking tape is a good starting point. If the canopy frames are straight then cut small pieces of tape, using a straight edge, and fill in the window area. If the frames have angles or are curved then lay on a apiece of tape that covers the window area and the frame. Burnish the tape, particularly around the frame lines. Take a sharp (I always use new) No 11 scalpel blade or similar (pointy) and carefully run it around the frame lines. The sharper the blade the easier it is. If it's dificult to see the frame lines then hold the canopy up to a light source. Take your time and watch your fingers. Paint the interior colour first (this will be seen on the inside) then the exterior colour. after gloss coates and matt coates, score around the edges of the tape, to cut through the paint and varnish, and carefully remove the masking. With care you will get perfect, or near perfect results every time. Like all techniques I would advise practice, use some old canopies. An alternative to Tamiya tape is 3M. The advantage of 3M is that it has a matt surface that when you burnish it down turns clear, this enables you to see the frame lines easier.
Something else that you might want to consider is dipping your canopies in Klear, Future in the US, it makes them sparkle.
Hope this helps.
Mal
P.S. Nice 219 SeanSki