In that case, you need to create Cash receipts by yourself and get it stamped and signed by your employer because those details are imperative. If you are below the TAX level then IT returns are not necessary but you will need to show 4 Cash payslips each year of the total work experience you claimed.
In addition, prepare a general Cash receipt certificate for each year which shows all the Cash salary received for each month of the particular year.
Lastly, these documents are not mandatory and it’s up to the visa officer’s discretion to request in the later stage of your application if needed. The one and only document you need for the proof of work is the REFERENCE LETTER, make sure you get that well polished. Go through the CIC website for more information regarding how to request an effective letter from your employer.