Now that the main body of the canoe is planked, I clamp the strongback to my desk, and sand the hell out of the entire outside of the boat.  I start with 100 grit sandpaper, and end up using 220 grit, to get rid of most blemishes.  The strongback keeps the canoe rigid while its sanded.  I save the sawdust created, just in case, to fill any huge mis-alignments or gaps, and mix it with the glue to form a type of putty, and re-sand if necessary, once I fill them in.  When its mostly smooth, I cut the extended stems off the strongback, and remove the canoe.