For the hollandaise sauce:
Combine the mayonnaise, 1 tablespoon warm water, mustard, lemon juice and cayenne pepper in a blender and process until combined. Scrape out and set aside.
For the eggs benedict:
Fill a wide pot with about 3 inches of water. And the vinegar and bring to a low simmer.
Heat the oil in a large nonstick pan. Add the Canadian bacon and shallots and cook, stirring frequently, until golden, about 4 minutes. Add the kale, remove from the heat and stir until the kale wilts, about 2 minutes. Season with pepper. Set aside and keep warm.
Toast each English muffin in a toaster oven or under a grill until lightly golden, about 5 minutes. Top each with a tomato slice and toast until the tomato is just slightly warm, about 1 minute. Top each muffin with the bacon-kale mixture.
Crack each egg into a mug and slip into the simmering water. Cook until the whites are at desired doneness, 3 to 5 minutes. Remove with a slotted spoon and place on each benedict. Drizzle with hollandaise and serve.