Fill a large bowl with cold water. Peel the potatoes. Cut into 1/3-inch-thick slices, then stack the slices and cut into 1/3-inch-thick sticks, adding the potato sticks to the bowl of water as you go. Soak at least 30 minutes and up to 24 hours. (This will help remove the excess starch from the potatoes and keep them from oxidizing.)
Fill a heavy stockpot with 1 1/2 inches canola oil; fit with a deep-fry thermometer and heat the oil over medium heat until the thermometer registers 325 degrees F. Drain the potatoes and pat dry to remove any excess water.
Add 2 handfuls of potatoes to the hot oil. (There should be at least 1 inch of oil above the potatoes.) Par-cook the potatoes until they are light brown, 5 to 7 minutes. Remove the potatoes with a slotted spoon, gently shaking off the excess oil; let drain on a rack. Repeat until all the potatoes are par-cooked.
Bring the temperature of the oil to 350 degrees F. Cook the potatoes again, 2 handfuls at a time, until golden brown, about 2 minutes. Remove from the oil with a slotted spoon, shake off the excess and season lightly with salt and pepper. Repeat until all the potatoes are cooked.