Your profile mentions Uptown. Greenway to the St. Paul side River Road all the way around along Shepard would be a good way to pick up this route. Fair warning, this route is NOT flat.
If you want a flatter route I'd recommend biking to Cannon Falls and then take the Cannon Valley Trail all the way in. I've never found the direct route via Hastings very fun or pleasant and have not biked that way in a number of years.