Turns out it was an internet hoax.  There has been no announcement of a sequel to the 2008 movie.  Evidently, false claims were posted listing different cities where the alleged sequel would be filmed.   Example:
Step Brothers 2 to Begin Filming in St Cloud, MN this Fall.– The long awaited sequel to the 2008 film, Step Brothers, is finally on its way. Will Ferrell and Adam McKay are once again collaborating on a script that should be finished this spring. All of the original cast including Will Ferrell, John C. Reilly, Richard Jenkins, Mary Steenburgen, and others are set to return.  - Hoax Slayers

St Cloud was listed as one of these filming locations.  So, if you were really looking forward to Step Brothers 2, you may have to wait longer or possibly forever.