I used to have the frost-plug heater, actually still have it, but one of the pins off the element burnt right off inside where the cord plugs in. When its really cold, below 0F, it would not start, and I would have to tarp over the engine area and put a heat-gun under there for an hour. That, and even when it was between freezing and 0F, the engine wasn't really warm, it was just a bit less-cold.
If a circ-heater is working properly, the engine will be actually warm, even if its ugly cold out. We use 1500watt circ-heaters on 15litre Cummins engines in equipment around the farm; Versatile 4wd, a Peterbilt, etc, and even though those installations are optimal with a heat-blanket and short hose run, the engines are warm to the touch after 4~6 hours of plug-in. Makes starting equipment to haul grain or plow snow in January much easier. If one is forward-thinking enough to park within cord-range, otherwise its a gen-set and some babysitting.
Yes, the way I'm set-up on my acreage near Edmonton, my Kubota is parked outside in a metal-building, which some days feels colder than outside.
Are you actually Toronto, or one of the GTA-suburbs? I have have cousin northeast of To, about halfway between Oshawa and Peterborough. I've been there during his maple syrup run, quite fascinating.
