For the eggs benedict casserole

• Grease a 3-quart baking dish with butter. Add English muffin cubes and chopped Canadian bacon; toss to combine and then spread the mixture evenly in pan. Set aside.
• In a large bowl, whisk the eggs. Whisk in milk, garlic powder, paprika, salt, and pepper. Pour the egg mixture evenly over the English muffin and Canadian bacon mixture. Cover and refrigerate overnight.
• Remove the pan from the fridge and let stand at room temperature for 30 minutes before baking.
• Heat over to 325 degrees F.
• Bake casserole, uncovered, until slightly puffed and egg mixture is set, about 50 minutes. Serve with tarragon béarnaise sauce.

For the tarragon béarnaise sauce

• In a small saucepan, combine the wine, vinegar, onions, and peppercorns. Bring mixture just to boiling then reduce heat and simmer until reduced to 1/4 cup, about 20 minutes.
• Strain mixture through a fine-mesh strainer into a bowl. Discard solids.
• In another small saucepan, whisk egg yolks and 1/4 cup of the white wine-vinegar reduction together until combined. Set the pan over very low heat and add 1 (4 tablespoons) portion of butter. Cook the mixture, whisking constantly and allowing the butter to slowly melt and incorporate into the egg mixture. Remove the pan from the heat occasionally if the pan gets too hot and eggs begin to curdle. When the first portion of butter is incorporated, add the second portion. Continue cooking and whisking until the butter is melted. Repeat with the remaining butter. Cook until the mixture thickens.  
• Stir in chopped tarragon leaves. Taste and season with salt to taste. Keep sauce warm until ready to serve (see Notes).