If you use payroll, commercial, or in-house developed software to manage your business, you can file 1 to 500 amended slips (610 Kb) over the Internet. For T1204 returns, the maximum file size is 700 slips (610 Kb).
Amended slips
These are slips that include changes to slips already filed. Amended slips are indicated in an XML file with report type code "A".
Cancelled slips
These are slips that were filed but must be removed. Cancelled slips are indicated in an XML file with report type code "C".
Cancelling a return
To cancel a return that you have filed, write to your tax services office.