CP received 3,500 single sheathed box cars in 1920 and 1921 that very closely followed the USRA design. The major differences were the 7/8 Murphy ends, and they had grain hoppers in the floor. Like many other Canadian single sheathed cars they also had grain clips (Rapido calls these siding clips) to help keep the lowest boards from bowing out when loaded with grain.
Rapido's model is accurate for cars from the mid-30s after the grain hoppers were removed, along with receiving Ajax handbrakes and AB brake appliances.
Tichy and Westerfield also have this variation available, and the same commentary applies as before. Both of them can be built with the grain hoppers. I should also point out that Tichy also makes a cement car modification, with hatches in the roof and floor that matches a D&H prototype. Until the Rapido cars are released I can't tell how easy it would be to use the Tichy parts to modify them.
Yes, I've already ordered one...