Hi JJ,
Have no problems holding either of them in any account type. They form a duopoly in Canada and you just can't find that type of moat in any other stock. So overall, you can buy either of them.
I've attached a picture that compares the two - i'd say both are fully valued with CNR holding a slight edge in terms of valuation but nothing that really sets either apart. CP has the better operating margins (typical has had better ones) which is a key metric in the industry. The other major difference - CNR's debt load is much less than CPs. CP is also going to be taking on more debt with its KC purchase.
All things to consider when deciding which to chose.
Mat