Efiling T1013 to CRA is a side function of myTaxExpress EFile software. You need to have CRA EFiler ID/Password first, and set them in software preference by menu "Start | Preference".
Next, you need to create an empty tax return for the client. Client's name and S.I.N information must be correct. Since T1013 doesn't include birthdate, marital status and tax province information, you can choose anything when creating such an empty tax return. Tax return is just a place to hold a form T1013.
Next, you need to add a form T1013 into this return by menu "Forms | add a tax form". Complete all the required information inside T1013.
You can only submit online access authorization through online filing. Note, please check the radio button beside "A. Authorize online access..." in part 2.
Last, you submit the completed T1013 to CRA by choose menu "Start | Submit T1013 electronically".
Last note, Filing T1013 will not contain any T1 tax return information to CRA.