It’s not the ‘canvas’ you’re thinking of, it’s the workspace area that surrounds the canvas.
If I have off-canvas content, which I sometimes do, I Resize the canvas (Image → Resize Canvas), with no offsets, to a suitably larger size so that original off-canvas content becomes visible on the new larger canvas.
Later, I Resize the canvas to the original size.
There are more details in my feature request topic here:
Request for Resize to Current Layer function
Edit:Add: Also, dredging my memory, I’m sure that @halla (the Lead Developer) once said that they had tried making off canvas content visible around the canvas and it became very difficult to do.