I've always thought using BareMetal Foil the easiest way of masking canopies.
Just stick a square of foil over the windows in question, burnish down with a cotton swab (q-tip), trim the edges you need to trim, then remove the excess foil.
You must burnish down the cut edges to prevent paint from bleefing under the foil. Noiw, just paint and then remove the foil. The stuff is so thin you can see every single little frame - much better than any tape I've used.
Cheers,
LeeTree