To be honest, I own CNR and this is a company I'm comfortable dollar cost averaging into at most prices.
Yes, on a historical basis it's a little expensive. At 17 times earnings, it's above the high 13, low 14 range it sits at. And a price to book of 5.5 is higher than the 4.5~ it typically sits at as well.
But, this is a blue-chip Canadian stock with a massive economic moat that has provided Canadians with rock solid returns for a long time.
However, It IS almost approaching overbought levels. It has a 14 day RSI of 69. So, we could see a short term pullback, but RSI's, much like any other technical indicator, are never 100% accurate.
Over the long term will you feel bad averaging in at these prices? In my opinion, no. But if you're willing to take the chance that the stock dips, but knowing you'll pay more if it doesn't, that's a route you can take as well.