Etymology: Obviously, Ontario is the name of a province. Lake Ontario is supposed to be named after the dragon Ontario (because he was imprisoned under it), and the province named after that.
Ontario is the dragon that Sari befriended, who was imprisoned under Lake Ontario by the Draçonic Council for his part in the Great Torment. At over 700 years old, he is still relatively young for a dragon, but being one of the last dragons alive, he is older and wiser than most beings. He was born the runt of his litter, small and weak and late for many dragon milestones (growing wings and being able to glide, then fly, then breathe fire). He was also unable to find the ashes required to develop fire breath when he gained his first breath ability (which almost all dragons choose as their first for its utility in combat), and instead only drank water, giving him the (seemingly useless) water breath ability. He ran away from his nest after that and met Sari, the first person who wasn't disappointed by him. Their friendship was very close, and brought the humankinds and dragons closer together. However, the Great Torment tore them apart again.