What do you mean by surname?
Your surname is your family name. It’s also called your “last name.” When filling out applications, type your surname as it appears on your passport, travel or identity document.
Do not use initials.
If you don’t have a family name on your passport, travel or identity document, enter all your given name(s) in the surname field and leave the given name field blank. Do not enter “Not applicable,” “*” or “NA.”
If you leave the given name field blank
If you’re applying to sponsor your family, you can’t validate Schedule A (eIMM 5669) with the given name field empty. If you need to leave it blank for the above reason, you can print it without validating it, and include a letter with your application explaining why you had to do this.
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=014&top=4
If entering both fields are mandatory, then enter your given name twice, once in the given name and then in the last name field