In case it has been overlooked, CN and CP have co-operated a number of times before:
From the IBI Report:
[...]
5.6.4
Encouraging Coproduction by the Two Major Freight Railways
Over the last couple of decades the two major railways have improved their efficiency by joint
use of trackage, called “coproduction” in the railway industry.
The first major implementation of
this was in the Fraser Canyon area of British Columbia.
Both CN and CP have single track lines
from Kamloops to Vancouver.
A double track railway provides much greater capacity than the
sum of two single lines and offers faster transit times.
CN and CP made an agreement whereby
the CN line is used by westbound trains and the CP by eastbound trains between Vancouver
and Kamloops.
Such coproduction agreements are in place in other parts of Canada including
between Parry Sound and Sudbury.
The new connections envisaged in this report would
also
prepare the way for coproduction to be
extended from Toronto to Sudbury on the transcontinental lines of the two railways
and perhaps
eventually eastward to Montreal.
[...]
https://www.milton.ca/MeetingDocume.../ENG-020-15 The Missing Link Final Report.pdf