Butter three 9-by-5-inch metal loaf pans. Punch down the dough and sprinkle it all over with the sunflower seeds. Scrape the dough out onto a generously floured work surface and knead it lightly, working in the sunflower seeds. Cut the dough into 3 equal pieces. Press each piece into a rectangle about 8 by 10 inches. Starting at a long end, roll up the dough, tucking in the sides neatly. Transfer the dough to one of the prepared loaf pans, seams down. Repeat with the remaining dough. Cover loosely with plastic wrap and let rise in a warm, draft-free spot until the top of the dough is just below the rim of the pans, about 1 hour.