I have a feeling that AC might look at both the A318 and the CRJ700/900, because they fulfil different aspects of what Air Canada is looking for.

With the DC-9 already gone, and the 737-200 and 146's on their way out, the two aircraft will be able to fill this whole nicely. The CRJ's will replace the DC-9's and 146's, while the 318 will replace the 737-200.