Add the water, oil, maple syrup, sourdough starter, salt, cinnamon, walnuts, and seeds to the bowl of a stand mixer. (That's everything but the flours). Use the kneading hook to mix it all together.
Add the whole wheat flour and mix again.
Add 1 cup all purpose flour and mix. Keep adding little bits of flour until the dough starts to pull away from the bowl.
Knead for 8 minutes.
Grease a second bowl. Transfer the dough to greased bowl and flip the dough around so that all sides are greased.
Cover and allow to rise in a warm place until doubled (about 3-12 hours depending on your starter).
If possible, perform a couple sets of stretch and folds at 30 minute intervals after mixing the dough.
Form into a loaf and place in a loaf pan or onto a baking sheet. Cover and allow to rise in a warm place about 2 hours.
Preheat oven to 400 degrees Fahrenheit.
Bake about 25-30 minutes or until crust is slightly brown and a toothpick inserted in the centre comes out clean.