In a large bowl, stir sugar into warm water to dissolve. Sprinkle yeast on top and stir in with a wooden spoon. Let sit for 5-10 minutes, until foamy.
Stir the olive oil into the yeast mixture. Add 8 1/2 ounces (2 cups, spoon and level) bread flour, 6 3/8 ounces (1 1/2 cups, spoon and level) whole wheat flour, seeds, and salt and mix together until a wet dough begins to form.
Gradually add the remaining 2 1/8 ounces (1/2 cup, spoon and level) whole wheat flour as needed, followed by the remaining 3 tablespoons bread flour as/if needed, working into the dough with a wooden spoon until enough flour has been added to knead the dough by hand. Throughout this process, add JUST enough flour to work with the dough without it getting stuck to your hands or your kneading surface. The dough should be somewhat sticky, so avoid adding more flour than necessary. Knead dough until fairly elastic, about 10-15 minutes.
Lightly oil a bowl about twice the size of the dough and shape dough into a smooth round. Transfer dough to bowl, turning once to coat both sides with oil. Cover with plastic wrap and leave to rise until doubled in size (about 60-90 minutes).
Grease an 8 1/2" x 4 1/2" loaf pan. Punch down the risen dough gently and knead briefly. Shape into a round and use palms to tuck edges of dough underneath, forming an oblong shape to fit in the loaf pan. Transfer to pan and cover with greased plastic wrap. Leave to rise until dough fills tin and reaches about 1 1/2" above rim of pan at highest point (about 30-45 minutes). Meanwhile, towards the end of this time, preheat oven to 425ºF.
For glaze, whisk egg white and water together and brush over loaf just before baking. Sprinkle extra mixed seeds on top.
Bake bread in preheated oven for 20 minutes, and then cover with foil (if needed, or once golden), reduce heat to 400ºF, and bake about another 10 minutes, or until the loaf sounds hollow when tapped at the base, and the internal temperature measured from the bottom of the loaf reads over 190ºF.
Transfer loaf to a wire rack to cool before slicing. Store in an airtight container or zip-top bag at room temperature.
*I used poppy seeds, white and brown sesame seeds, chia seeds, and pumpkin seeds. Any mixture you want to use will work!