For the pork:
Pour 2 cups of the simmering water into a 6-quart heatproof container with a tightfitting lid, then remove the remaining water from heat. Add salt and sugar to the heatproof container and stir until dissolved. Add garlic, chiles, peppercorns, and pork. Top with remaining 8 cups of now-tepid water to fully cover the meat. Submerge the meat if necessary by filling a resealable bag with water and placing it on top. Cover and refrigerate 12 hours or overnight.
When the pork is ready, remove from the liquid, rinse, pat dry with paper towels, and place fat side up in a roasting pan. Allow to come to room temperature for about 30 minutes. Meanwhile, heat the oven to 400°F and arrange a rack in the middle. Roast pork until the internal temperature reaches 165°F, about 1 hour 45 minutes. Let cool to room temperature, at least 45 minutes, then slice thinly, about 1/8" thick.
For the pickled carrots & daikon radish:
Combine vinegar, sugar, and salt in a small saucepan over medium heat. Once sugar and salt have dissolved, remove from heat, add carrots and daikon radish, and stir to coat in pickling mixture. Let stand until carrots have softened, at least 2 hours or overnight. Drain well and set aside.
Slice off the top 1/3 of the baguettes lengthwise and set aside. Remove enough of the bottom interiors so that the filling can fit easily.
Spread mayonnaise on each baguette’s upper 1/3 and on each bottom. Spread half of the paté on each bottom section, then top with sliced pork (there may be some left over), cucumber, cilantro leaves, pickled carrots, daikon radish, and jalapeños. Sprinkle each sandwich with toasted peanuts and soy sauce and close with the upper parts of the baguettes. Place 10 toothpicks approximately 1 inch apart to secure the sandwiches and slice into about 6 sandwiches. Serve.