It is interesting you mention this. I believe at this point AC is the bigger threat to Cargo Jet especially as the company recently announced their intentions to expand their cargo business.
I won't re-hash all the details - but here is a good article that summarizes AC's plans from a couple of weeks ago: https://theloadstar.com/air-canada-plans-a-dedicated-freighter-fleet-to-expand-cargo-business/
Then today, AC issued this release: https://aircanada.mediaroom.com/2020-11-27-Air-Canada-Provides-Update-on-Cargo-Business
It has announced a new VP of cargo and ratified its union contract with the pilots to enable cargo delivery. These are big steps and one can argue it is taking direct aim at Cargo Jet which has soared to all time highs this year. Too soon to tell how it will fare, but it appears the company is now going all in on cargo.
It is also worth noting, that cargo is likely to increase given the huge shift to eCommerce and there is likely room for both of these companies to growth in this environment. However, i view AC as the more aggressor in this situation.
Mat