CRA provides an example of a designated related-group entity filing a single T1134 for the group

Regarding the situation where Canco transferred all the shares of USco (which, in turn, wholly-owned a US LLC) to a newly-incorporated Canadian holding company (Holdco) on a s. 85 rollover basis; and then USco was wound up into Holdco before the end of the same taxation year (a June 30, 2023 year end for both Canco and Holdco), CRA indicated that since Canco and Holdco each held the USco shares directly for a portion of their 2023 taxation year, each would be a reporting entity that was required to file a T1134 for their 2023 taxation year. However, as a related group with the same year end, and using the same functional currency, they could designate one of them as their representative to file a single T1134 information return with the required information for both.

Neal Armstrong. Summary of 10 October 2024 APFF Roundtable, Q.4 under s. 233.4(4).