Step 1 Combine the oils in a deep pot. The oil should be 8 inches deep; if it's not, add more canola oil to bring it to that depth. Set the pot over medium heat and bring the oil to 275 degrees.
Step 2 While the oil is heating, combine the flour, cornstarch, sugar, cayenne pepper, salt and black pepper in a wide mixing bowl.
Step 3Dredge the squid and the lemon slices, 4 to 6 pieces at a time, in the flour mixture, shaking off the excess flour before gently lowering the pieces into the hot oil. The pieces should bubble and sizzle but not splatter; lower or raise the flame accordingly. Cook until they are golden brown and crisp, about 5 minutes. Keep an eye on the temperature and do not let it rise above 280 degrees.
Step 4Use a slotted spoon to transfer squid and lemon slices to a paper-towel-lined tray. Season with more salt and pepper while the pieces are still hot out of the oil. Serve hot, garnished with the lemon wedges.