Fill a large, wide pot halfway with water and bring to a boil. Add the vinegar and reduce the heat until the water in the pan has no more bubbles.
Crack the eggs very close to the surface of the water and gently drop them in. Cook for 3 to 4 minutes. Using a slotted spoon, remove the eggs to a bowl of cold water. Reserve the eggs in the cold water and reserve the poaching liquid to reheat the eggs. (Obviously, if you're poaching the eggs a day ahead, you can reheat the eggs in new water!)
Coat a large saute pan lightly with olive oil and heat to medium. Add the Canadian bacon slices and cook on both sides until hot but not brown.
Toast the English muffins. Place 1 slice of Canadian bacon on each English muffin half.
Warm up the egg poaching liquid (or a pot of new water if you're poached ahead) and place the eggs in the water for 1 minute, or until the eggs are warm but not cooking any further. Remove the eggs with a slotted spoon, blot with a paper towel or tea towel, and place on the English muffin halves. Top with Hollandaise Sauce.
Toss the mesclun with lemon juice, big fat finishing oil and salt. Garnish each plate with the dressed greens.
Melt the butter over medium heat in a small saucepan. While the butter is melting, skim off the froth that accumulates on the surface. Simmer for 15 to 20 minutes, then gently ladle the clear butterfat into a measuring cup or small pitcher with a spout; this is clarified butter. Be sure to leave the milk solids in the bottom of the pan.
Combine the vinegar and peppercorns in a small saute pan and cook over a medium heat until almost all the vinegar has evaporated. Remove the pan from the heat, toss in a couple of ice cubes and let sit until melted.
Whisk the egg yolks in a medium metal bowl until frothy and fluffy. Strain the peppercorn liquid into the egg mixture.
Fill a medium saucepan with 1 inch of water and bring to a simmer. Place the metal bowl on top of the saucepan and gently cook the eggs for 2 to 3 minutes, whisking frequently.
Very slowly begin to whisk in the clarified butter. Start with 2 or 3 drops and continue with a couple more drops after the butter is incorporated. Continue adding the butter a little at a time until all of it is incorporated and the sauce is fluffy and foamy. If the eggs seem to be cooking too quickly, pull the bowl from the saucepan and lower the heat. If the eggs start to curdle, immediately toss in an ice cube to cool them down.
Once all the butter is combined, add the lemon juice and season the sauce with cayenne and salt.