For anything you've ever wanted to know about CN steam-era boxcars see -
While I acknowledge CN cars would have likely to be seen less frequently on the T&NO than, say, the GN or Maine Central, the fact is the CN (and CP) represented a very large percentage of the North American boxcar fleet - so many that it's hard to imagine not having one or two show up on a railroad, even in the deep south.
Search the list archives for never-ending discussions of "boxcar percentages" and "freight car fleet percentages" and similar terms and you'll see how much time and effort has been expended on statistical research and sheer speculation on this topic.
So if you include one or two CN cars in your car fleet no one vaguely familiar with steam era freight car distribution would bat an eye. But the cars represented by the Accurail cars are not a terribly large percentage of the CN car fleet, meaning that if you want to have one or two Canadian National cars I don't think either of them should be the Accurail car, especially if you're modeling any time after 1940 or so.
CN had the single largest fleet of 40'-6" 10-panel steel cars built to the "1937 AAR" design (with some of them having unique variations of ends and roofs.)
If you wanted to have one or two representative CN cars for a late steam era/transition era road those would be the ones I'd suggest.