Season beef liberally with salt and pepper. In large Dutch oven or heavy ovenproof pot over moderately high heat, heat oil until hot but not smoking. Add beef and sear until dark brown and crisp on both sides, about 10 minutes total. Transfer beef to large plate. Pour off oil in pan and discard. Add sherry and simmer uncovered, scraping up browned bits on bottom of pan, until reduced by half, about 5 minutes. Pour reduced sherry into a heatproof liquid measuring cup.
In same pan, combine carrots, onions, celery, garlic, and bay leaf. Lay beef on top of the vegetable mixture and pour in the reduced sherry. Add enough chicken stock to cover 3/4 of meat. Cover and place on lowest rack in the oven. Roast until fork-tender, about 3 hours.
While beef is roasting, prepare roasted carrots and caramelized onions. During final hour of roasting, in large bowl, toss carrots with olive oil until well coated. Season generously with kosher salt and freshly ground black pepper. Spread on baking sheet and transfer to upper rack in oven. Roast until slightly tender and browned, about 45 minutes. Remove from the oven, transfer to large bowl and keep warm. During final 30 minutes of roasting, place a heavy 12-inch skillet over moderately high heat, add the canola oil and heat until hot but not smoking. Add onions and saute, stirring constantly, until caramelized, about 20 to 25 minutes. Season, to taste, with kosher salt, add to roasted carrots in large bowl, and keep warm.
When beef is tender, transfer to serving platter and tent with foil. Skim fat from liquid in pot. Strain liquid through fine-mesh sieve, pressing on solids with back of spoon to extract all juices, then discard the solids. Return liquid to pot, set over high heat, and bring to boil. Reduce heat to moderate and simmer, uncovered, until reduced slightly, about 5 minutes. Season juices to taste with salt and freshly ground black pepper. Pour half of juices into bowl with carrots and onions; toss to combine. Pour the other half of the juices into gravy dish. Arrange carrots and onions around beef on a serving platter and serve immediately, with extra juices on side.