The officer can bring out a K-9 unit for a basic sweep as long as they do not unreasonably extend the purpose of the traffic stop.  A K-9 sweep is not akin to a usual "search" in that the dog is only smelling the air around the vehicle-- which any person can technically do-- so there is not the offensive invasion of privacy.  An officer doesn't have to have any information on which to base a sweep-- however, if they are going to continue a traffic stop beyond the usual time frame, they do need to have some information from somewhere that you are using or delivering controlled substances.  The information can come from another officer or from a confidential informant and they are not required to disclose where the info came from prior to executing the sweep.