if son from girlfriend in Pakistan while working there, but I'm canadian citizen, and now married someone else in Pakistan and submitted spousal sponsorship, and also didn't mention about son in application will be there any issues.
you are married and your son in your current spouse step son......and the principal applicant, your spouse is expected to declare their step children in IMM5406.
SECTION B
Write the personal details for your children. It is very important that you list all of your children (even if they are already permanent residents or citizens of Canada). This includes:
married children,
adopted children,
children of your spouse(step-children) or common-law partner,
any of your children who have been adopted by others,
any of your children who are in the custody of an ex-spouse, former common-law partner or other guardian.