Yes, you can absolutely write on the canvas! Just make sure to use a paint pen or a sharpie for best results, to avoid smudges.  Please note that if you don't intend to write on the canvas, that any inks will likely not wipe off after being written on the canvas; we also don't recommend using anything other than a lightly dampened cloth to clean canvas, as any cleaning solution or a lot of water, could damage your canvas.