I have done some riding in the Rocky Mountains, in the Laurentians, and on the East Coast of Canada.
The hardest climb was on the back side of Mt McKay on the First Nations land South of my home town of Thunder Bay, Ontario.
https://www.google.ca/maps/@48.30542...!3m1!1e3?hl=en
The road is mainly a gravel service road up to Lock Lomond, the municipal water supply for Thunder Bay South (Fort William), but this particular climb is so steep that it is paved, presumably so service vehicles can get up it, and probably to prevent erosion in the rain.
The other fun fact about this climb is that, before you reach the climb, the ride through the community of Fort William First Nation is (was) an exercise in outsmarting or outrunning a bunch of unleashed dogs. Then you climb about a third of the main access road to the lookout on top of the mountain before turning off onto the service road.