What's the difference between the Resize The Canvas and Rescale The Painting options?
Resize The Canvas change the size of the canvas you're painting on but not the paint itself. With Resize The Canvas it is possible to cut parts of your painting if you resize to a smaller value than the picture you've painted. And you also can add additional canvas to have more space to paint on.
Just think like having a real canvas with a nice painting on it and you cut it with a scissor... OK... adding canvas is in real not so easy
Rescale The Painting change size of the canvas and the size of the paint on the canvas.