Don't be tempted to screw in the canopy directly... it WILL deform over time if you do.

If you go with something like cap screws or wood screws, I highly suggest getting the smallest grommets you can find. ( Grommets work much better than fuel tubing for this... )

Make a small hole where the grommet will go using a Dremel stone pointed tip bit. This will smooth the hole edges without causing any cracks.

Widen the hole to just under the diameter of the grommet and slide the grommet in place.

You can also use a servo collar ( supplied with most servo mounts ) within the grommet.

Then put the screw or cap screw through the grommet using a washer.

The screw should push the grommet out a bit as it tightens fixing the canopy in place.

There will be just enough give on the grommets to prevent warping over time.

The downside will be that the canopy will be held a bit higher than the airframe, though this may be slight enough that you will not care.

The same technique works well for affixing cowls.