Chandigarh Railway Station is well connected to Bus Station by Normal/Volvo City Buses.
Auto too ply but better to await for Volvo, for a comfort ride. Auto may cost Rs. 150 (after tough negotiation) while Volvo may cost Rs. 30/40 (not sure)!!
In case of operator, its State Undertaking Service only (Haryana, Himanchal, Punjab, UP, Rajasthan State Transport). Volvo run is deployed by most Undertakings, whose timing may vary. Isuzu also run by Himachal Transport. If not Volvo, then look out for Haryana Roadways, as they follow schedule strictly!!