In 1948 ,the CNR got 50 covered hoppers like the one shown below., although the one in the photo is missing its hoppers:
In the same year, the CPR began receiving slab-sided covered hoppers from National Steel Car, similar to the Sylvan car shown below. The CN also ordered these cars, starting in 1951, along with the TH&B in '56,and the PGE in 1962.
True Line offers pretty-well all versions of the slab-sided cars - there were variations in the sides (some with cut-outs, others without), number of roof hatches, and, of course, paint schemes. While they were fairly pricey, I did see them occasionally at around $20.00.
The CPR had quite a few boxcars with underfloor hoppers, but no roof hatches. These were "convertible" cars, with drop-down doors to cover the hoppers when the car was used as a boxcar, but they could be considered an early covered hopper, I suppose. The original two date from 1911, with another 200 delivered in 1912-13 and were 36' Dominion/Fowler cars, while in the '20s they constructed 3500 40'-ers. These cars were intended mainly for grain service. CP built their first true covered hopper in 1919 - I can't find the article on it, but I believe it was a variation on their "Big Otis" gondolas.
Also in-service in Canada from about the mid-'30s were carbon black covered hoppers, similar to the Rail Shop Inc. car shown below. Due to the nature of the lading, these cars were used only for transporting carbon black: