Preheat the oven to 250°. Place the roast on a baking sheet or roasting pan. Rub with 1 tablespoon olive oil and cover with Montreal steak seasoning, patting the seasoning into the meat.
Cook the roast for 2 to 2 1/2 hours or until Rare (120°) to Medium 140°. Remove from the oven and cool to room temperature. Cover and refrigerate. (I do this because it's easier to slice the roast very thinly when the meat is cold).
Make The Caramelized Onions
Peel the onions and and slice them into 1/4 inch slices. Heat the remainder of the olive oil in a heavy pot or dutch oven (with a tight fitting lid) over medium heat. Add the onions and a pinch of kosher salt to the onions. Stir to combine place the lid on the pot. Simmer the onions, stirring occasionally for about 1-2 hours, or until onions are soft and golden.
Transfer the onions to a storage container and refrigerate until ready to serve.
Assemble The Sandwiches
Place the cold roast beef on a carving board and use a very sharp carving knife to slice the beef very thinly. Set aside.
In a saucepan, combine the consommé water and sherry. Heat to a simmer and taste for seasoning. If it's too salty for your tastes, add a little more water. Keep on a simmer
Preheat the oven to 350°. Split the hoagie rolls lengthwise and place them on a baking sheet. Fill the rolls with two slices each of provolone cheese and place them in the oven for 3-5 minutes or until the cheese just starts to get melty.
Reheat the caramelized onions in the microwave for 1-2 minutes. Set aside.
Using a pair of tongs transfer about half pound of the beef to the simmering jus. Heat for 30-40 seconds in the jus and use the tongs to transfer and pile the meat onto the prepared hoagie roll.
Top each sandwich with a scoop of caramelized onions.
Divide the jus into 6 ramekins and serve alongside each sandwich for dipping.