To prepare stuffing, cook leek in boiling water 2 minutes. Drain and plunge leek into ice water; drain. Pat dry with a paper towel. Place leek, bell pepper, corn, and crab in a large bowl; toss gently to combine. Combine mayonnaise and next 4 ingredients (through egg white) in a small bowl, stirring with a whisk. Add mayonnaise mixture to crab mixture; toss gently to coat. Gently fold in parsley and tarragon; set aside.
Preheat oven to 375°.
To prepare lobster, bring 5 quarts water to a boil in an 8-quart stockpot; plunge 2 lobsters headfirst, 1 at a time, into water. Return to a boil. Cover, reduce heat, and simmer 2 minutes. Remove lobsters from pan using tongs; drain well. Repeat procedure with the remaining 2 lobsters. Cool lobsters slightly. Remove claws; place claws on a baking sheet. Cut the lobsters in half lengthwise; clean upper cavity of lobsters, leaving white meat intact.
Arrange lobster halves, cut sides up, on a jelly-roll pan coated with cooking spray; spoon 1/2 cup stuffing into cleaned upper cavity of each lobster half. Top stuffing in each lobster half with 1 tablespoon cornflakes, and lightly coat with cooking spray.
Place baking sheet with claws on bottom rack in oven; place jelly-roll pan with stuffed lobster halves on upper rack in oven. Bake at 375° for 20 minutes or until lobster halves are done and stuffing is lightly browned. Remove the lobster halves from oven; cover and keep warm. Bake claws an additional 10 minutes or until done. Cool claws slightly; remove meat from cooked claws.
To prepare vinaigrette, combine orange juice and remaining ingredients, stirring with a whisk. Serve vinaigrette with lobster.