Prep the Cabbage: Carefully remove 8 large outer leaves from the cabbage.
In a large pot of boiling water, cook the leaves for 4-5 minutes, just until they are limp and pliable.
Drain well.
Using a small knife, carefully shave down the thick vein on the back of each leaf so it's flush with the rest of the leaf.
Set these aside.
Shred 4 cups (960 ml) of the remaining cabbage and place it in the bottom of a 3. 5 to 6-quart slow cooker.
Create the Filling: In a medium bowl, combine the rinsed beans, cooked rice, onion, celery, carrot, and garlic.
Stir in 1⁄2 cup (480 ml) of the marinara sauce to bind the mixture together.
Assemble the Rolls: Lay a blanched cabbage leaf flat.
Place about 1⁄3 cup (720 ml) of the bean mixture onto the center of the leaf.
Fold in the sides, then, starting from an unfolded edge, roll it up snugly.
Repeat with the remaining leaves and filling.
Mix the Sauce: In another bowl, whisk together the remaining 3 cups (720 ml) of marinara sauce, raisins, lemon juice, and brown sugar.
Layer and Cook: Pour about half of the sauce mixture over the shredded cabbage in the slow cooker and stir to combine. Gently arrange the cabbage rolls on top.
Pour the remaining sauce evenly over the rolls.
Slow Cook to Perfection: Cover and cook on LOW for 7 to 9 hours or on HIGH for 3. 5 to 4. 5 hours. To serve, carefully remove the cooked cabbage rolls and serve them with the shredded cabbage mixture from the pot.