The CRA is scheduled to re-open their NETFILE service on Monday, February 22, 2021. You can come back and file your return then.
This FAQ tells you how to submit your tax return to CRA using the NETFILE service in TurboTax Online: https://turbotax.community.intuit.ca/community/federal-taxes-netfile/help/in-the-online-edition-of-turbotax-how-do-i-submit-my-tax-return-to-cra-using-the-netfile-service/00/873715