Should see Maritime Ontario (yard in Saint John just west of town), Bison Transport (took over Celadon's intermodal business in eastern Canada) and potentially Armour (based out of Moncton, but very unhappy with just CN service) containers coming up as well in the near term. AxSun has been moving some volumes more recently with CP and the TFI group of companies (Clarke, and others) has been doing some more as well. I'd look at the CN 120-121 domestic volumes, typically they are on the head pin of the train (all the 53s) with some manifest that gets dropped off at Moncton for Saint John.
What's interesting is CN owns TransX and H&R, but they as of now have still moved containers on CP. It's a surprising move, while yes the railroads do compete with the IMCs to some degree, CN's purchase of IMCs like that might really drive other IMC's off their network and onto CP. My understand too is a lot of companies have been asking for alternatives to CN in Moncton, so it's not surprise that this has started up rather quickly.
I wouldn't be surprised too if some MSC boxes move spot on CP, as they seem to hedge volumes back and fourth with CN & CP. The CMA contract is firmly on CN for now. Alliance wise, you could see some Maersk, COSCO, and Evergreen boxes moving spot as well, although I think that is less likely.
I'd keep an eye out too for Temperature control containers too (CP ones), as Loblaw is a large Canadian grocery distributor and retailer.