Ok, so I've seen many people say that Elmer's glue works best for canopies and clear plastic, but why is that a good glue to use?

I don't know about elmers, but white glues have advantges :
- some become translucid when set
- if you spill a bit on the canopy, you just need to clean it away. It won't be smeared.
- they don't create fumes while setting. CA glue creates fumes that smear the canopy.

Same reasons as penpen. It dries clear and doesn't mar the plastic, but I will also add that it's easy to find, you can use it for other things than models, and it is cheap. White glue is also useful for filling small gaps, as a substitute for putty.

Nic