Liberally butter a 2-quart shallow baking dish.

Split and toast the English muffins. Cut each in half creating four half moons. Cut the Canadian bacon into half moon slices as well.

Arrange the muffins and bacon in the baking dish cut sides down. Evenly sprinkle with mushrooms and green onions. Top evenly with the two cheeses.

In a large bowl, combine the remaining ingredients whisking until well combined. Carefully pour the egg mixture into the baking dish making sure that each muffin is covered with liquid.

Cover the prepared dish tightly with plastic wrap and refrigerate for at least 2 hours, preferably overnight.

When ready to bake, remove the strata from the refrigerator and heat the oven to 350 degrees. Place the baking dish on a baking sheet and cook until puffed and the center is set - about 1 hour, 15 minutes to 1 hour, 30 minutes. Tent the dish with foil if the top starts to brown too quickly.

Let stand 10 minutes before serving.