I thought I would try some of the things I learned on a pair of white canvas slip-ons for my son.
I used Sharpie Fine Point and Ultra Fine Point pens.
I tested spray fixative and ScotchGuard on a piece of canvas with some Sharpie drawings. The fixative faded the black and the ScotchGuard made it bleed.
I decided to leave them as is and let them age at will.