If you used NETFILE to file your tax return, you should have received a 6 digit confirmation code from the CRA. This number is provided by the CRA, and confirms they received your tax return.
You can also confirm that they've received your return by logging into your "My Account" on the CRA's site, and checking the status of your return. There is typically a delay from the day you NETFILE, or mail, your return to when it shows up in your "My Account".