I've thought about this for a while now too. Although I never seen my payara jump, I've heard otherwise and this kinda goes for many species such as arowanas, african tiger fishes, etc. Basically any powerful fish that has the ability to jump.
And I'm in the same boat as you -- if I should make a modification, not only does it have to be functional, but needs to be easy on the eyes as the minimum. I thought about using latches, locking the canopys to the aquarium frame.. only thing is I'm trying to figure out something that wouldn't make it a hassle to open every time I need to feed or do maintenance.