GTW did not have any sleepers so any sleeper on a CN/GTW through train would be CN. Every once in a while you would see some CN head end cars on the Maple Leaf, International Limited and the Intercity Limited, usually express refers. While I have not seen CN coaches on these trains it doesn’t mean it didn’t happen. Dinners were GTW and usually did not cross the border, they were pulled off in Lansing.
I hope that this helps.