Preheat oven to 375°F (350°F for sea-level). Grease the cavities of a donut pan, and set aside.
In a medium bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. In a smaller bowl, whisk together the buttermilk, canola oil, artificial vanilla extract, and egg whites. Add the wet ingredients to the dry ingredients, and stir until just barely mixed (a few dry spots are ok). The donut batter will be the same texture as a thick pancake batter.
Using a rubber spatula, gently fold the rainbow sprinkles into the batter until there are no dry spots (don't overmix)! Spoon the batter into a large piping bag (or a plastic bag with the tip cut off).
Pipe the batter into the donut pan cavities about 1/2 way full (don't go more than halfway, or the batter will rise too much and you won't get a hole in the center). Bake for about 9-10 minutes, until a toothpick comes out clean.
Let the donuts cool in the pan for about 5 minutes, and then let them cool completely on a rack. Dip each cooled donut halfway into the glaze, letting the excess glaze drip off. Decorate as desired, and let the glaze set completely, about 20 minutes. Serve! Store extras in an air-tight container for up to three days.