Thanks Ray
Actually now CHC-I has changed the system for medical assessment , they have given it to International Organisation of Migration (IOM). There Health division is responsible to conduct medicals of Canadian visa applicants and they dispatch it to New Delhi. They deals in several other countries too. Their offices are in Islamabad, Karachi and Lahore. I don't know when this system started. You can book appointment at any center which you feel close to your city. I live in lahore so i did my medical from lahore office.