If Canada Revenue Agency tells you that they are reviewing your Tax returns, it simply means that amount you are claiming is accurate or not.Most of the times it is a routine procedure and there is no need to panic.
Also, these Tax reviews are not audit.
As Canadian Tax system is based on self-assessment and you usually don’t need to include any document while filing the return.So from Time to Time, CRA contact individuals under their review programs.
You must ensure to give requested documents from CRA as soon as possible so that it can complete the review process quickly.Once CRA completes the review, it will let you know the result either via writing, in letter or Notice of assessment or Reassessment.So if you have any more tax payable CRA will let you know and you should pay that tax as soon as possible.
In case you cant pay that tax in one go.You can let CRA know and it can work with you to set up a payment arrangement.
Also, you need to keep all your documents for at least 6 years.If you have claimed any tax credits or deductions in the past, you need to keep all the relevant documents and receipts with you for at least 6 years.
You can read more at :