In a medium bowl, whisk together the corn flour, rice flour, tapioca starch, sugar, baking powder and salt. In a small bowl or measuring cup, whisk together the buttermilk and egg; add it to the dry ingredients and whisk until smooth.
Place some rice flour in a shallow bowl. Bring a couple inches of canola oil to 350-375F in a wide heavy pot.
Thread hot dog halves onto popsicle sticks and douse them in rice flour, then dip in the corn flour batter to coat. Carefully place into the hot oil and cook a few at a time (don't crowd the oil, or it will cool it down), turning often with tongs, until golden on all sides. Remove and place on a paper towel-lined plate to drain.
Serve warm. Makes about 1 dozen corn dogs.