It is difficult, infect very difficult visa to obtain and getting impossible for an ordinary man. You require a lot of documentation and still there are so many chances you would be refused.
Once you have decided to apply, you need to obtain an application package which you can download from the web, click here.
If you are applying from Pakistan, you need some additional documents, especially Supplementary Information Form, download here.
Further, make sure you have included the documents listing at the Canadian High Commission's Website, click here.
They also demand an affidavit from the applicant to affirm on oath the correct reason and other circumstances fro visiting Canada. Also get the Fee Receipt Green Form photocopied twice and attach with the application.
Submit Your Application
Once you completed your application, attached the required documents, paid the correct fee, go to either TCS or Gerry's Express Office and post for submission to High Commission. To read further, how to post your application, please click here.
Don't forget to read the entire section published at the Canadian High Commission's Website for applying for Temporary Resident Visa, click here.
I hope this would help you to apply properly for a Canadian Visit Visa.
Sarfraz Ali Advocate