What an interesting train! On point is 2 CP GP38-2s and behind them is a large dimensional load with 2 spacer cars on each end and behind that is the CP weed spraying train doing its work, as seen in photo by the spray coming off the train.
As said by CP
Confined to our right-of-way, this program includes vegetation control on the ballast portion (graveled section) of our right-of-way. Safe rail operations require our ballast to be free of weeds and brush, which can hinder rail maintenance and can be a hazard to the public and our employees. If left uncontrolled, vegetation contributes to trackside fires, impairs visibility of train signals, impairs sight lines at railway crossings, impairs proper inspection of track infrastructure and creates a generally unsafe workplace.
We use herbicides to control grass and weeds on the ballast and any remaining brush is also sprayed to eliminate it from the ballast.
More info can be found here - http://www.cpr.ca/en/community/living-near-the-railway/ontario-spray-schedules