CRA Auto-Fill is currently unavailable due to system maintenance being performed by the Canada Revenue Agency. This service will be available as of February 24, 2020, when NETFILE officially opens.
I can also confirm it is not working - at first I thought this was due to CRA, but realized the page that is giving the 503 service unavailable error is coming from turbotax website itself:
This seems to be a recurring problem. Stopped Mar 25 in the afternoon after I completed 2 returns and is still down Mar 26 morning. Are you sure this isn't software?
If you are using TurboTax Online please try changing your browser then try again. You can also sign in to your CRA "My Account" on a different web page and then try CRA Auto-Fill once again.
It is working for most people unless you try at a time where the server is overloaded.