Thanks George, railroader9731 and Gus for taking some of your valuable time to reply.
With your help I think I found the right CN coal hopper:
Bowser Mfg - Pennsylvania Class GLa 2-Bay Open Hopper w/Accumate Couplers; Ready to Run -- Canadian National (brown)
Pennsy's Home-built Hoppers in N Scale from Bowser ? Pennsy's first all-steel hoppers were built in 1898 by Pressed Steel Car Co. but design flaws and production backlogs convinced Pennsy to construct their own improved version, the home-built GLa class. These hoppers became a PRR standard with over 30,000 built between 1904 and 1920. The cars lasted into the 1960s and a few remained in work train service into the 1980s. The GLa class was one of the most common coal hoppers in North America, so they'll look right at home on your steam- or early diesel-era layout. Ready-to-run GLa Hoppers from Bowser come equipped with AccuMate(R) knuckle couplers and feature authentic paint schemes. ?
Any coment about that choice ? I think it'll look good coupled to a CN GP7
Jacques