Preheat the oven to 350°F. Grease a 9x13-inch baking dish with cooking spray.
In a large mixing bowl, whisk together the eggs, milk, Dijon mustard, salt, black pepper, and cayenne pepper until well combined.
Layer the cubed English muffins evenly in the prepared baking dish. Top with the diced Canadian bacon, followed by the shredded cheddar cheese and chopped chives.
Pour the egg mixture evenly over the layers in the baking dish, ensuring all the bread is soaked.
Cover the dish with aluminum foil and let it sit for 15 minutes to allow the bread to absorb the egg mixture.
Bake in the preheated oven for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the casserole is set and lightly golden on top.
Drizzle the hollandaise sauce over the casserole before serving.
Let the casserole cool for a few minutes before slicing.