HOLLANDAISE SAUCE: Vigorously whisk the egg yolks and lemon juice together in a stainless steel bowl and until the mixture is thickened and doubled in volume. Place the bowl over a saucepan containing simmering water (or use a double boiler) the water should not touch the bottom of the bowl. Continue to whisk rapidly. Be careful not to let the eggs get too hot or they will scramble. Slowly drizzle in the melted butter and continue to whisk until the sauce is thickened and doubled in volume. Remove from heat, whisk in cayenne and salt. Cover and place in a warm spot until ready to use for the eggs benedict. If the sauce gets too thick, whisk in a few drops of warm water before serving.
Meanwhile, brown the Canadian bacon in a medium skillet and toast the English muffins, cut sides up, on a baking sheet under the broiler.
Fill a 10-inch nonstick skillet half full of water. Add white vinegar to the cooking water. (This will make the egg whites cook faster and not spread.) Bring to a slow boil. Gently crack 1 of the eggs into the water taking care not to break the yolk. Repeat with remaining eggs. Reduce the heat to a gentle simmer. Cook 3 ½ minutes until the egg white is set and yolk remains soft. Remove with a slotted spoon, allowing the egg to drain.
TO ASSEMBLE: Lay a slice of Canadian bacon on top of each muffin half, followed by a poached egg, season with salt and pepper and spoon hollandaise sauce over the eggs. Garnish with chopped parsley, if desired.