If this is a Post Graduate Diploma in IT then I believe it's better for you to send both your qualifications to WES. They will assess it and "may" give a Canadian equivalence of Two or More certificates, diplomas or degrees considering one of them must be a program of 3 or more years.
Since you don't have a Masters then you should send both qualifications. Currently WES requires only the highest qualification to be sent. If a candidate has Masters then they are not required to sent their bachelors degree. If WES needs more documents they will request the applicant to submit.
If you graduated from April 2006 onwards, please visit
National University of Singapore’s website and follow the steps to retrieve your OpenCerts documents. Please include your OpenCerts documents as email attachments and send them to
submit@wes.org. The email subject should be National University of Singapore and your WES reference number.
If you graduated before 2006 or if you are enrolled in a program, please contact
the Registrar’s Office to ask them to send your documents directly to WES in a sealed envelope that is signed or stamped across the back flap by the appropriate official at the institution.
University may require a formal request form. here it is
https://applications.wes.org/onlineapp/pdf/ca/International_Transcript_Request.pdf
I hope this helps you