As the two others have suggested small magnets are the best option, get some like these:

http://e-magnetsuk.com/magnet_produc...d_magnets.aspx

I use the EP642 version (5mm x 10mm) as these give you something to get hold of to remove when needed as the pull on these tittle puppies is amazing.

I trim the canopy using a pair of scissors designed for flower cutting, these have a serrated edge to the blades which is great when cutting plastics and canopies as it 'grips' the plastic as it cuts so making it easier to cut in a controlled manner. The serrated edge you are left with also acts as a great surface for the epoxy to bond to. Tack it in first in a few spots and then once these are dry lift the edge of the canopy and feed in a thin bead of epoxy around the edge of the canopy keeping it as close to the cut edge as possible (syringe with a thin cyano type nozzle is good for this) so any wicking does not travel past the frame edges - pop the magnets all over the frame to 'clamp' the canopy to the frame and voila - jobs a gooden.........

marcs