Pat the chuck roast dry with paper towels and season all over with salt and pepper. Use a small knife to make small slits in the roast and insert the garlic slices.
Heat 1 tablespoon of olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Carefully place the roast in the pot and sear for 3-4 minutes per side, until well browned. Transfer the roast to a plate.
Add the remaining 1 tablespoon of olive oil to the pot. Add the chopped onion and cook for 3-4 minutes until softened. Add the carrots and mushrooms and cook for another 5 minutes, stirring occasionally.
Pour in the balsamic vinegar to deglaze, scraping the bottom of the pot to lift any browned bits. Stir in the tomato paste, Worcestershire sauce, and dried thyme. Cook for 1 minute until fragrant.
Add the cranberries, beef broth, and maple syrup to the pot. Stir to combine, then return the seared roast and cooked vegetables to the pot.
Bring the liquid to a boil, then reduce the heat to low. Cover the pot and let it simmer gently for 3.5 to 4 hours, or until the meat is very tender and shreds easily with a fork. For tenderness, the internal temperature should reach 190-205°F (88-96°C).
Carefully transfer the roast and vegetables to a serving platter and cover to keep warm.
Make the gravy. Skim any excess fat from the surface of the liquid in the pot. In a small bowl, whisk together the cornstarch and cold water to create a slurry. Whisk the slurry into the pot and bring the liquid to a simmer. Cook for 2-3 minutes, stirring, until the gravy has thickened.
Slice or shred the pot roast and serve with the vegetables and gravy.