Make a canvas active so that you can paint on it, view and modify its layers, delete it, and so on. Or pick it so you can transform or delete it.
Only one canvas can be active at once. This is the canvas on which new layers are created.
When a canvas plane is first created, it is active by default.
Only the layers of the active canvas are displayed in the Canvas Layer Editor. (See Windows > Editors > Canvas Layer Editor).