Step 1Combine 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 2While 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.