Hey there!
Back when we built these portfolios in late 2018, we actually found CP to be trading at more attractive valuations. That's primarily why it was added to the portfolio and not CNR. And, it looks like we were right. Since inception of those portfolios CP has returned 80% while CNR 35%.
Now I'd say they're both pretty evenly valued.
Canadian Pacific did have some operational issues back in the day and as a result it doesn't have nearly as strong of dividend growth as Canadian National Railway does. In fact, CP Rail just got its Dividend Aristocrat status back with 5 consecutive years of growth. Compare this to CN Rails 25+ years, and you can see who's been more reliable in that department.
Moving forward in my opinion I think both railways will perform relatively the same, so I would opt for the stability of a company like Canadian National Railway over Canadian Pacific. However, both are very solid options.