1600 km³ × .1 kcal/ℓ is 670 petajoules, so that's the energy input you'd need to heat the lake up by 0.1°. World marketed energy consumption is about 20 TW, so the entire world economy could heat the lake up at about 0.23° per day if you covered it in a blanket first. So it's not completely out of the question, but only 2.7 million people live in Toronto, so Toronto probably only uses about 20 GW.
By comparison, the lake's surface area is 19000 km², so when the sun is shining on it (at a slanting angle, as it always does that far north), it's receiving about 10 TW of solar energy, half the amount used by the entire human economy. It reflects about 10% of that into space and converts the rest into heat, then re-emits it as longwave infrared light, half at night.
By comparison, the lake's surface area is 19000 km², so when the sun is shining on it (at a slanting angle, as it always does that far north), it's receiving about 10 TW of solar energy, half the amount used by the entire human economy. It reflects about 10% of that into space and converts the rest into heat, then re-emits it as longwave infrared light, half at night.