Both eastbound and westbound Canadians have a service stop and crew change at Jasper AB. Ninety minutes are scheduled, but apart from allowing time for the different service functions e.g. washing the windows of the consist, it also provides a bit of a cushion to gain back on the schedule.
If the delay - most of it on account of CN Rails practice to give freight the preference - is within reason. Recovering more than four hours delay - as happened on the return trip - is an impossibility.