Spray a 9x13-inch baking dish with cooking spray.

In a large bowl, whisk together the eggs, 2 cups of milk, chopped green onions, onion powder, and salt until well mixed.

Layer half of the diced Canadian bacon in the prepared baking dish.

Spread the diced English muffins evenly over the bacon layer.

Top with the remaining Canadian bacon.

Pour the egg mixture evenly over the entire casserole.

Cover the baking dish tightly with plastic wrap and refrigerate overnight.

Preheat the oven to 375 degrees F (190 degrees C).

Remove the plastic wrap from the casserole.

Sprinkle the paprika evenly over the top of the casserole.

Cover the casserole with aluminum foil.

Bake in the preheated oven for about 30 minutes, or until the eggs are nearly set.

Remove the aluminum foil.

Continue baking for about 15 more minutes, or until the eggs are completely set and the casserole is golden brown.

While the casserole is baking, prepare the hollandaise sauce.

In a saucepan, whisk together the hollandaise sauce mix and 1 cup of milk.

Add the margarine to the saucepan.

Bring the mixture to a boil over medium heat, stirring frequently.

Reduce the heat to medium-low and simmer, stirring constantly, until the sauce thickens, about 1 minute.

Remove the casserole from the oven and let it rest for a few minutes.

Drizzle the prepared hollandaise sauce generously over the top of the casserole before serving.

Serve immediately.