Doesn't matter. Some trucks come from the factory with air horns, some with electric. As long as they don't play alternating tones (dual tone is ok as long as they sound at the same time) and are under the noise limit you are good.
In addition to what you've already quoted;
Horn
83(1) A person shall not use the horn or other audible warning device of a motor vehicle, motor cycle, moped, power bicycle or bicycle
(a) except for the purposes of giving notice to other persons that are on or approaching a highway or within the vicinity of the vehicle, or
(b) so that it makes more noise than is reasonably necessary to give notice to other persons that are on or approaching a highway or within the vicinity of the vehicle.
(2) A person operating a motor vehicle, motor cycle, moped, power bicycle or bicycle shall sound the vehicle’s horn or other audible warning device whenever it is reasonably necessary to warn persons on or approaching the highway in the vicinity of the vehicle.
Basically as long as you have some sort of horn, which can be controlled on and off at will, and you don't use it like a ReRe, it is fine. The ones that play music are not fine (see previous sentence).