Canvas is forgiving right up until the moment it is not. The two things that ruin a canvas tote are soaking it and drying it with heat, and both are easy to avoid.
Start dry
Empty the bag, turn it out and shake the seams. Most of what makes a canvas bag look tired is dust and grit sitting in the corners, not staining. A soft brush along the seams removes more than any wash will.
Spot clean before you wash
Mix a little mild detergent into cool water, dip a white cloth — white, so you can see what is lifting — wring it almost dry, and work the mark from the outside inwards. Rubbing outwards spreads the stain into clean fibres. Let it dry and repeat rather than scrubbing harder.
Only wash the whole bag if you must
If the whole bag needs it, hand wash in cool water. Do not put a structured or printed tote in a machine: the agitation breaks down the interfacing that gives the bag its shape, and prints crack. An unlined, unprinted plain canvas tote survives a cold gentle cycle, but nothing more.
Drying is where bags die
Never tumble dry, and never dry a canvas bag on a radiator or in direct sun. Stuff it loosely with a towel or clean paper so it holds its shape, and let it air dry away from heat. Heat shrinks canvas unevenly and the bag will never sit square again.
Hardware
Dry metal fittings immediately. Water sitting around a rivet or a zip base is what causes the rust spots that later bleed into the fabric.
