Preheat oven to 375°F (190°C) and grease a baking dish.
Spread bread cubes evenly in the dish and sprinkle Canadian bacon on top.
In a bowl, whisk eggs, milk, salt, and black pepper.
Pour the egg mixture over the bread and meat, pressing gently to soak.
Bake uncovered for 35–40 minutes, until eggs are set and top is lightly golden.
While baking, melt butter for the sauce. Whisk egg yolks, lemon juice, and mustard, then slowly whisk in melted butter until smooth.
Serve casserole warm with hollandaise-style sauce spooned on top.