Unfortunately, you can't just wash bleach out as if it were a stain. When you spill bleach on colored fabric, it removes the dye, leaving the bare fabric. However, all is not lost. Depending on how big the spot is, there are several ways to "fix" black canvas shoes.
Color in the spots with a black Sharpie pen. This may be one of those few times when the easiest method is the best. A color-fast fabric marker may work even better. If you happen to spill bleach on a less common color, get a color-fast Pantone marker from an art supply store. You can probably match any color exactly.
Bleach the shoes completely. If the black marker shows up even at a distance, you may want to bleach the rest of the shoes. Soak them in a standard bleach at a ratio of four parts warm water to one part bleach for no more than ten minutes. You may need to repeat the application with the same formula if the color isn't satisfactory. Afterward, use a bleach neutralizing agent such as antichlor (sodium thiosulfite) or three-percent hydrogen peroxide. Otherwise, the bleach will keep eating away at the canvas.
Re-dye the shoes. If you need the shoes to be black, you may have to re-dye them. Start with bleaching both shoes. If you don't, those bleach spots will come out lighter than the rest of the shoe even with a heavy black dye. Rinse off the bleach thoroughly with the antichlor neutralizing agent. Then, use a standard fabric dye that you would use for pants or shirts.
Make a design on your shoes. An alternative to a full bleaching of your shoes is a lower-strength bleach gel pen. This will allow you to draw on your shoes, incorporating the original bleach spots into your own design. Or, you can use the bleach gel pen to completely remove the black. Just work the bleach into the canvas, then wash the shoes and allow them to dry. You will probably need to repeat the bleach pen if you want to remove all the dye, as the gel is purposely made to a lower concentration than undiluted bleach. Afterward, you should still douse the shoes with antichlor or hydrogen peroxide to remove the residual bleach.
Eliminate yellowish stains. If in the process of using bleach on canvas shoes you are left with yellowish stains, make a paste of baking soda and water and apply it to the shoes. Let it sit overnight. Wash the shoes the next day. Applying hydrogen peroxide straight to the stains is another way to get rid of them. Half a cup of cream of tartar in a quart of hot water also provides a solution.
Use gloves when working with bleach.
Never use vinegar in combination with bleach.