Preheat oven to 425 degrees. Spread four slices of bread with approximately 1/2 tablespoon butter each and lay, buttered side down, on a baking sheet.
Using a 3-inch round biscuit cutter, cut a hole out of the center of the remaining slices of bread and lay on top of the buttered slices on the baking sheet.
Break 1 egg at a time into each of the 4 holes. Evenly distribute Canadian bacon, tomatoes and cheese over the tops of the eggs. Season with salt and pepper.
Transfer to oven, and bake until the cheese is melted and the egg whites are set, about 15 to 17 minutes.