Melt butter in large sauce pan over medium heat. Add onion, garlic and sugar; cook for 1 to 2 minutes or until onion is soft. Add broth, water, salt and pepper; bring to a boil, stirring occasionally. Reduce heat to low. Cook, stirring occassionally, for 15 minutes.
Stir in pumpkin, evaporated milk and cinnamon. Cook, stirring occasionally, for 5 minutes. Remove from heat.
Transfer soup to blender or food processor (in batches if necessary); process until smooth. Return to pan, heat through if necessary. Serve warm.