Waxing the inside and outside of the canopy, 'might' work but how do you get the wax from the inside of the canopy off?
Dipping the canopy in Future, or other high gloss varnish, is intended to protect/improve the canopy, but like you, I've had mixed results.
It would help prevent the fumes from the CA etching the clear plastic, but this is not guaranteed.
Other options would be to use a different glue specifically for canopies?
Deluxe Materiels: AD12 CANOPY GLUE or DELUXE AD57 ROKET CARD GLUE,
Alene's "Clear Gel Tacky Glue", Gator Glue, Micro Crystal Clear, Humbrol ClearFix, ZAP, Formula 500, some low-odour CA's...
The list is endless... perhaps suggesting there is no single product that works on everything.
I have had most success with Deluxe Materiels or Gator Glue though, & at least these are harmless to the canopy if you need to errr re-do.