Here is an article that lists key differences. Good luck with your submittal!Since self-employed work does not qualify for CEC, IRCC's concern is clear - they want to distinguish if you were a 'employee' or a 'contract hire'. The latter does not require the employer to deduct Employees Insurance (EI) premiums, CPP/ QPP contributions and Federal Income tax.
So your response should primarily focus on documents that provide direct evidence of your being an 'employee'.
Does your Paystub (as well as your T4) show amounts deducted for Employees Insurance (EI) premiums, CPP/ QPP contributions and Federal Income tax?
If yes, it will be easier to show you were an 'Employee' versus a 'Contract' hire.
Since the tax filing deadline is only a day or two away, you should have received your T4's from your employer. The T4 is likely to be more convincing than just a pay stub as its simply harder to fake. So apart from the other documents you intend to submit - make sure to include your T4's and cover this logic in a solid Letter of explanation (LOE).
https://www.thebalancesmb.com/are-you-a-contractor-or-an-employee-2948639