detect empty canvas space in fill it with content-aware tool

yes there is.

1. flatten the document before you change the canvas (you now have only the background layer.)
2. copy the background layer to a new layer
3. extend the canvas as you want it
4. select layer contents
5. inverse the selection
6. do content-aware fill
7. deselect
8. stop recording the action

you're done.

I have some ideas, there isn't a default native method that comes to mind as I type.

Have all images had their canvas resized? Or is there a mixture of images?

Was the canvas extended with transparent pixels, or opaque pixels such as white?