While holding the Exacto knife with the blade edge away from the shoe, cut strands of the canvas by plucking at them individually. Make a line about an inch or so long.
Be careful not to cut into the mesh. Don't worry if you cut a few threads of the mesh. It is pretty resiliant to unravelling. If you do cut a big slit in the mesh, use some matching thread and stitch it back up after the all canvas has been removed.