Fill a large 12-inch skillet nearly to the rim with water. Add the white vinegar and 1 teaspoon of salt, then bring to a boil over high heat.
Once boiling, remove the skillet from the heat.
Crack an egg into a small bowl. Gently pour the egg into the skillet. Repeat with the remaining eggs, being careful not to overcrowd the skillet. Consider poaching only 6 eggs at a time.
Cover the skillet and allow the eggs to poach until the whites are set but the yolks remain slightly runny, about 5 to 7 minutes.
Using a slotted spoon, transfer the poached eggs to a paper towel-lined plate to drain.
Preheat the broiler on your oven.
Place the split and toasted English muffins on a baking sheet, cut side up, and top each with a slice of Canadian bacon.
Broil the English muffins and Canadian bacon until the bacon begins to brown, about 1 minute.
Place one poached egg on top of each English muffin and Canadian bacon assembly.
For the Hollandaise, in a large heat-resistant bowl, whisk together the softened butter and egg yolks.
Set the bowl over a medium saucepan containing 1/2 inch of barely simmering water, ensuring that the bowl does not touch the water.
Gradually whisk in the 1/2 cup of boiling water and continue to cook, whisking constantly, until the sauce thickens and reaches 160 degrees Fahrenheit, which should take about 7 to 10 minutes.
Remove the bowl from the heat and stir in the lemon juice and cayenne pepper, if using. Season with additional salt to taste.
Spoon 1 to 2 tablespoons of the prepared Hollandaise sauce over each poached egg.
Garnish with minced fresh parsley and serve immediately.