The day before you plan to serve this, spray a 9x13-inch baking dish with cooking spray.
Cut the toasted English muffins into 1-inch chunks. Cut the Canadian bacon into 1-inch pieces. Layer half the Canadian bacon in the bottom of the prepared dish. Top with the English muffin chunks, then with the remaining Canadian bacon pieces.
Separate the yolks from the whites of 4 of the eggs. Put the yolks in an airtight container and refrigerate until it is time to make the hollandaise sauce. Put the egg whites in a large mixing bowl with the remaining 6 whole eggs, ½ teaspoon dried mustard, 1 teaspoon salt, the pepper, paprika, and milk. Whisk to combine. Pour the egg mixture over the muffin chunks and Canadian bacon. Cover with plastic wrap and refrigerate overnight (8-12 hours).
About an hour before planning to serve the dish, preheat the oven to 375°F and remove the casserole from the refrigerator. Remove the plastic wrap and cover with foil. Bake for 40 minutes, remove the foil, and continue to bake for 20 minutes or until the top is nicely browned and the casserole is set. Let cool 5 minutes before serving.
While the casserole is cooling, make the hollandaise sauce. Put the reserved egg yolks in a blender with the remaining ½ teaspoon dried mustard, remaining ½ teaspoon of salt, lemon juice, and hot sauce. Blend for 5 seconds. Remove the small plastic top from the blender lid and, with the blender running, slowly drizzle in the melted butter. Continue blending until all the butter has been incorporated. The sauce can be kept warm, if needed, by placing in a heatproof bowl over barely simmering water, making sure the bottom of the bowl is not touching the water. (It takes so little time and effort to make the hollandaise, I usually just whip it up while the casserole is cooling.) Put the sauce in a small serving bowl and serve with the casserole.