Using grater, coarsely grate potatoes. Transfer to colander, rinse with cold water, and allow to drain. Complete same procedure with onions; mix together with grated potatoes. Press with paper towels to squeeze out remaining liquid. Transfer mixture to large bowl; add eggs, flour, salt and pepper and stir gently to combine. In large nonstick skillet over moderate heat, heat 3 tablespoons canola oil until hot. Drop 4 (1/3 cup) portions batter into pan and gently flatten each into disk. Fry, turning once, until well browned on both sides. Transfer to paper towels to drain. Serve immediately.