Technically speaking, the CRA’s NETFILEservice is for people who prepare and file their own returns and isn't intended for people filing returns on behalf of others. But, it's understood that many people trust their spouse/partners, friends, and family to prepare their returns for them.
If you’ve been entrusted by a family member or close friend to file their taxes for them using NETFILE, you can certainly do so in TurboTax. Ideally, the taxpayer (i.e. the person for whom you’re preparing a tax return) makes a final review of their return and together you transmit the return to CRA’s NETFILE service.
If you prepare more than 20 tax returns on behalf of others, and/or collect payment for preparing returns for others, CRA considers you a professional tax preparer. Professionals preparing returns for others are supposed to use CRA’s EFILE service (not NETFILE).
For more information about the restrictions that the CRA places on its NETFILE service, read the NETFILE eligibility page on the CRA’s website.