Canvas in World Space

I think that stacking Canvasses and having one per enemy is not a good idea.

You should have one Canvas and have it interact with all enemies.

The point here is that the Canvas links in to everything with the Event System so there is no need to have it as a child.

As an example, I have multiple Aircraft Carriers of which the player ship is teleported to at the start or on respawn. The Active carrier pokes the (single) Canvas and takes control of the Launch button. Pushing the button with launch the ship from that one carrier alone. The theory goes here that you can only be docked at one at a time so they can share a button.

Of course, Im not sure what your situation is here but if you can achieve something similar it will be to your advantage and save a lot of processing.