I think U can attach the medical with ur visa app itself bcoz i did so and got my visa in 8 working days. It speeds up the whole process and I am not sure if that can be followed in Pak , atleast in India it works and on the cic site it has been recommended to attach with the application. The medical practitioners are authorised by the CHC , find ur one with this link http://www.cic.gc.ca/dmp-md/medical.aspx . Call med practitioner to ask any of ur queries. Alll lthe Best.