Preheat oven to 375°F and spray a 9x13 inch baking dish with cooking spray.
Spread half of the diced English muffins evenly in the bottom of the dish, then top with half the diced Canadian bacon.
Repeat with the remaining English muffins and Canadian bacon to create a second layer.
In a mixing bowl, whisk together eggs, milk, melted butter, ground mustard, onion powder, garlic powder, salt, and pepper.
Pour the egg mixture evenly over the layers in the baking dish and cover tightly with foil.
Bake covered for 30 minutes, then remove the foil and bake an additional 15 minutes or until the casserole center is set.
Let the casserole cool for 5 minutes before cutting into 8 pieces.
Warm hollandaise sauce gently in a saucepan over medium-low heat or in short bursts in the microwave, stirring frequently.
Drizzle the warmed hollandaise sauce over each casserole piece and garnish with fresh chives or a dash of paprika if desired.