AA did, you will recall, retain some code-share rights on CP for the next 10 years, although that does leave the rest of oneworld out in the cold.
I personally doubt they're looking for a Canadian partner-who could they choose? At this point if they can either fly direct to the few big Canadian cities, or route passengers on AA, that can suffice. But losing CP does rather put 1W in a distant 3rd alliance in Canada, way behind Star and NW/CO as far as offering connections and destinations.
You guys also overlooked Royal Aviation. They're not as big as Transat or C3, but they do have a lot more diverse operations, and seem to have more interest in the domestic traffic. I could see Royal becoming a major player in domestic travel, although WestJet is taking a pretty good run at that segment, too. None of the charters would join 1W, of course, but just thought I add Royal to your list of "wouldn't joins" so as its not forgotten.