Lightly coat a skillet with nonstick cooking spray. In the skillet, lightly brown Canadian bacon over medium heat. Transfer half a slice of bacon to each muffin half.

In a large skillet, combine 2 inches of water and the vinegar. Bring water to a boil and turn off heat. Lightly coat a small bowl with nonstick cooking spray. Crack one egg into bowl and gently slide egg into skillet. Repeat with each additional egg, one at a time. Cover skillet and let eggs stand for 3 to 5 minutes, or until set. With a slotted spoon, carefully remove eggs from the water, letting excess water drain. Place eggs on top of bacon.

In a heavy medium saucepan, whisk 1/4 cup of the buttermilk, the cornstarch and salt until smooth. Whisk in egg and remaining 1/2 cup buttermilk. Cook the sauce, whisking constantly, over low heat, until it comes to a simmer. Cook, whisking, for an additional 15 seconds. Remove from heat and whisk in lemon juice and butter. Spoon hollandaise sauce over eggs. Sprinkle with parsley and serve immediately.