Preheat the oven to 350 degrees F (175 degrees C). Spread bread cubes out onto 2 baking sheets.
Bake in the preheated oven until bread cubes are dry and lightly toasted, about 10 minutes. Transfer to a large mixing bowl.
Melt vegan butter in a saucepan over medium-high heat. Add celery and onion and saute until vegetables are softened but celery still has a bit of snap, about 5 minutes. Season with parsley, sage, thyme, garlic powder, salt, pepper, rosemary, and marjoram. Cook and stir for 1 more minute. Stir in vegetable stock and bring to a boil, stirring occasionally. After it reaches a boil, remove from heat.
Pour stock, vegetable, and herb mixture over bread cubes in the mixing bowl. Stir gently until well combined. Cover the bowl with aluminum foil and let sit for 5 minutes. Remove foil, fluff stuffing with a fork, and serve.