(1) Go to this below listed link
http://www.cic.gc.ca/english/e-services/mycic.asp
(2) Click on continue to Gckey
(3) If You've already account created, login with your Username and Password otherwise Click on Sign up to go on next page and create your username, password and security questions.
(4) After creating my CIC account, click link application to this account.
(5) Then select category as Temporary residence and subcategory as Visitor.
(6) Then select Family name, given name and date of birth option.
(7) Fill your family name(surname), given name and date of birth as per Passport or Application form.
(8.) Next in applicant personal info panel fill Passport information only and DO NOT FILL CITY AND COUNTRY OF BIRTH.
(9) Enter your date of visiting and leaving canada given on your invitation letter.
(10) Enter balance amount for expense you showed to visit Canada
(11) Next search for your application.
(12) Your application will be found and can be linked.
(13) You can get real time updates on your paper application online.
Note : In 24 hours you can try only 5 times to link your application and if you exceed that then you have to wait for 24 hours, so be careful about that.