So, first thing is referring to widgets on another card. This is easy, for a canvas named canvas1 on a card named card1 it's just card1.widgets.canvas1 (although if you have spaces in the names it is a bit messier)
The second issue might be that from my understanding, flipbook is designed for having all the frames in one image together, rather than split across multiple canvases. So you may need to rearrange how you've got the frames, i.e. combine them all into a single canvas rather than each in their own widget.