Combine 2 cups flour, ground mustard, yeast and salt in a large bowl. Heat milk, water, butter and syrup until very warm (120-130°F). Gradually add to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Add egg, egg yolk and 1 cup flour; beat 2 minutes at high speed. Stir in enough remaining flour to make soft dough. Knead on lightly floured surface until smooth and elastic, about 8 to 10 minutes. Cover; let rise 10 minutes.
Divide dough in half; roll each to 15 x 8-inch rectangle. Spread evenly with Sausage-Cheese Filling. Beginning on long end, rollup tightly as for jelly roll. Pinch seams and ends to seal.
Place on large greased baking sheet, curving ends to form a horseshoe. Repeat with second roll. Cover; let rise in warm, draft-free place until doubled in size, about 1 hour.
With sharp knife, make 5 diagonal slashes, about 1/4-inch deep through the surface. Brush with Maple Glaze; sprinkle with mustard seeds. Bake at 400 for 15 to 20 minutes or until done. Place baking sheet on rack and cool for 20 minutes. Serve warm.
Sausage Cheese Filling: Cook sausage over medium-high heat in a skillet until browned, stirring to crumble. Add bell pepper and onion; cook until tender, about 5 to 10 minutes, stirring frequently. Let cool. Stir in cheese.
Maple Glaze: Combine melted butter and maple syrup in a small bowl. Stir until well blended.