Bill, I use a variety of adhesives on canopies, depending on whether it will be permanently fitted
before, or
after, painting the model.
If fitted
after painting the model, then I normally use PVA, obtained in a 500 ml bottle from the local stationery store for around £1 (about 1/6th of the price of a comparable size "modelling" product, which is the same stuff !).
This can then be reinforced, if the joint allows, with Tamiya Extra Thin Cement, by running the tip of the brush carefully along the joint, once the part has set. The joint is then sealed and blended - in using a thin bead of PVA, applied using the tip of a cocktail stick, and any excess wiped off with a wet finger tip, or the cocktail stick tip, again wet. If required, this seal can then be painted to match the surroundings.
If fitted
before painting the model, for example where a windscreen needs to be fitted and the cockpit masked for spraying, then a combination of adhesives are used, as explained in the text for the pic below..
Spitfire !/32nd scale windscreen, canopy and rear glazing.
In this instance, due to the nature of the cockpit opening, it was 'safer' to fit the windscreen and rear glazing before spraying the model, and use the canopy, which would be displayed open on the finished model, as a mask, along with the cockpit door.
The door was temporarily fitted, being attached with PVA, allowing it to be easily removed later, and the clear parts masked using Tamiya masking tape.
The windscreen was fitted in the following sequence:-
1.) A thin bead of Revell Contacta Professional cement was applied along the front lip of the cockpit, using the nozzle on the cement bottle, and then carefully spread, thinly, along the lip, using a cocktail stick (Thick red arrow). A small spot of the same cement was carefully applied at the edge of the side lip, where it meets the cockpit door (thin red arrow), both of these areas being chosen as they were fairly large, and less chance of cement getting onto the clear parts that are masked.
2.) A bead of PVA was then applied around the remaining area of the windscreen sill (thick black arrow), and the windscreen fitted in place and lightly pressed down, adjusting as required. Once set, the joints were sealed with a thin bead of PVA (thin black arrow).
3.) The rear glazing was then fitted in the same manner, with the blue arrow indicating where Tamiya Extra Thin cement was carefully brushed into the joint, which was again sealed with a bead of PVA once set.
4.) The edges of the windscreen frame, and the tops of the door and fuselage sills, then had PVA applied, again using a cocktail stick, and the canopy was set in place, and adjusted to ensure the front and lower joints were correct. Once set, the front and rear joints were sealed with a thin bead of PVA (thin black arrow) in order to prevent any paint mist entering the cockpit when spraying.
Once the model has been painted and clear coated, the canopy and door can easily be removed, and the dried PVA carefully peeled off.
This method was used in order to provide more strength to the joint to fuselage for the windscreen and rear glazing, thereby preventing the parts coming loose when the paint-covered masks are removed after painting.
Hope his helps.