Hi Duncan,

I started looking into getting EFILE registration, and CRA still has information about XML transfer listed on their website.
https://www.canada.ca/en/revenue-agency/services/tax/trust-administrators/t3-return/how-file-t3-retu... 

1. Download the schema or use your software to create and save your return in XML format. If your file size is more than 150 MB, you may have to send fewer returns per file.
2. Make sure you have your web access code and your trust account number. If you do not have your web access code, you can get one at Web access code.
3. To submit electronically, go to Internet file transfer (XML).
   
   Any further comments or thoughts on this matter?  It appears that CRA is still promoting the use of 'your software' to create and save a return in XML format.