Grease a 9x13-inch baking dish with butter and set aside.
Split open each English muffin and then cut each piece in half. Arrange the slices on a baking sheet and drizzle with 2 tablespoons melted butter and bake until golden brown, about 10 to 12 minutes. Remove from the oven and let cool slightly.
Place half of the English muffin pieces in the prepared baking dish. Top with half of the Canadian bacon. Repeat with the remaining bread and bacon.
In a large bowl, whisk together the milk, eggs, salt, pepper, onion powder and garlic powder. Pour into the baking dish, over the bread and bacon. Cover with foil and chill for at least 4 hours or overnight.
Remove from the fridge and allow to sit while you preheat the oven to 375°F.
Bake covered 35 minutes. Remove the foil and bake until the casserole is golden brown and a knife comes out clean when inserted in the middle, about 15 to 18 minutes.
To make the hollandaise sauce, whisk the egg yolks and lemon juice in a large bowl until pale and doubled in size. Place over a pot with barely simmering water and cook, stirring constantly, until the egg yolks have warmed through, about 5 minutes. Keep the heat low and continue to whisk so as to not cook the eggs. Slowly whisk in the melted butter in a slow steady stream until the mixture comes together smoothly and has doubled and thickened. Season with salt and cayenne pepper. Cover and keep warm until ready to serve. If the sauce thickens too much as it sits, you can whisk in a tablespoon or so of warm water to loosen it up.
Once the casserole is done, remove from the oven and allow to cool for 5 minutes. Top with the warm hollandaise sauce and garnish with chives and paprika before serving.