I'm in St. Paul too. Have you been down the trail that starts down at the SW end of Harriet Island? It's paved, usually pretty debris-free (I'm a road biker, often on my hybrid), and heads down into Lilydale then into Mendota, and connects with the Big Rivers Regional Trail:
http://www.co.dakota.mn.us/parks/rivers.htm

It's not trafficked much, surprisingly. Often a few walkers/runners on it. Fairly flat. Quite scenic, as it goes along the Mississippi River.