On finely detailed n-scale models they are present and you can add to the “Additional Markings/Slogan” field.
CN's railway network in the late 1980s consisted of the company's Canadian trackage, along with the following U.S. subsidiary lines: Grand Trunk Western Railroad (GTW); Duluth, Winnipeg and Pacific Railway (DWP); Central Vermont Railway (CV) and a former GT line to Portland, Maine, known informally as the Grand Trunk Eastern. Canadian National America now also incorporates the Illinois Central purchased in 1998. On May 2003, BC Rail (BCR) became part of CN. On December 31, 2011, CNA completed the merger of Duluth, Missabe and Iron Range Railway Company; Duluth, Winnipeg and Pacific Railway Company; and Wisconsin Central Ltd. into its Wisconsin Central Ltd. Subsidiary. CN now covers coast to coast along with the Gulf of Mexico.
The CN group uses XYZ-nnna where:
X is the manufacturer:
Y is the type of use:
Z is the configuration of the locomotive (this parameter may be absent) :
nnn — two or three digits:
a — the sequence in which the members of a given class were ordered by CN. The first batch of locomotives of this type received are normally assigned "a", then "b" for the second batch, and so on. Note: (this parameter may be absent)
The bulk of my information was obtained from CNRHA, which has a wealth of information available. I do not know who prepared the list but would like to acknowledge their work. The Canadian National Railways Historical Association (known as the CN Lines Special Interest Group prior to 2010) was founded in 1989 as an international operational research and historical group that exclusively focuses on the Canadian National family of railways and promotes the art of modelling them accurately.
VIA Rail uses the CN designations.
The following is an explanation about the CP system by Steve Boyko, Confessions of a Train Geek, http://blog.traingeek.ca/2016/08/locomotive-classifications.html
CP's system is simpler than CN's, DYY-nna
Also note that CP doesn't always put a class designation on its locomotives.