Heat the oven to 350°F and butter a 9-by-13-inch dish. Toast the muffin pieces on a sheet pan for 8 minutes, then place them in the dish with the Canadian bacon.
Whisk the whole eggs, milk, salt and black pepper. Pour over the filling and let soak for 15 minutes.
Bake for 30 to 35 minutes, until the center reaches 165°F. Rest for 10 minutes while you make the sauce.
Whisk the pasteurized yolks, water and lemon juice in a heatproof bowl set over barely simmering water, keeping the bowl above the water. Whisk for 3 to 5 minutes until thick enough to leave a brief trail.
Remove from the heat and slowly whisk in the warm melted butter, then the cayenne. Spoon the hollandaise over the cut casserole portions and serve immediately; keep the sauce out of the oven.