Whisk agave syrup into warm water in a small bowl; add yeast. Let stand until yeast softens and begins to form a creamy foam, about 5 minutes. Whisk in eggs and oil.
Combine quinoa flour, sorghum flour, tapioca starch, salt, and xanthan gum in the bowl of a stand mixer. With the mixer running on low speed, pour in yeast mixture. Mix until dough is smooth, 2 to 3 minutes. Add sunflower seeds; mix until incorporated.
Line an 8 1/2x4 1/2-inch loaf pan with parchment paper; pour in dough. Cover with plastic wrap. Let rise in a warm, draft-free space, 30 to 45 minutes.
Preheat oven to 375 degrees F (190 degrees C).
Bake loaf in the preheated oven until browned and an instant-read thermometer inserted into the center reads 210 degrees F (99 degrees C), 50 to 60 minutes.
Invert loaf onto a wire rack and cool completely, about 1 hour, before slicing.