You will get buses to Amritsar from Jalandhar ISBT which is in city. Jalandhar Cantt does not have any bus stand.
You will get ordinary buses every 5 min and Volvo's available every 30 min of frequency. If you want Volvo services you can book through online www.punbusonline.com
www.pepsuonline.com
www.orbitbus.in
If...
more... you coming from Jalandhar cant you can get a bus from PAP Chowk, where all buses to Amritsar from Jalandhar bus stand stops here.