Please go to this link and download the required forms.
http://www.canadainternational.gc.ca/pakistan/visas/forms_temporary_resident_temporaire_formulaires.aspx?lang=eng&view=d
Once all the forms are filled up. take these forms with you to any Standard Chartered Bank branch in Pakistan and submit the fees. For single entry it was 75$ and for multiple entry its 150$. you have to submit in Rupees. check this out
http://www.canadainternational.gc.ca/pakistan/visas/fees-frais.aspx?view=d
You will recieve a green(or yellow dont remember exactly) reciept from the bank which you will put in the package to sent. once all the documents are ready, send them to the following address through TCS or Gerry's. make sure you include the passport in the package.
High Commission of Canada
Immigration Section
Sector G-5, Diplomatic Enclave
P.O. Box 1042
Islamabad, Pakistan
here is the link where you can find all information step by step.
http://www.canadainternational.gc.ca/pakistan/visas/visit-visite.aspx?lang=eng&view=d
Thanks!