Originally Posted by nli007

What is considered as "Uncontrollable" within the context of COVID-19 cancellations has guidance from the CTA via Determination No. A-2020-42 actually (Link: https://otc-cta.gc.ca/node/569158) It states:[8] Section 10 of the APPR provides a non-exhaustive list of situations considered outside the air carrier’s control (the third category above). These include medical emergencies and orders or instructions from state officials. In the context of the COVID-19 pandemic, the following would be considered outside a carrier’s control:

• flight disruptions to locations that are covered by a government advisory against travel or unnecessary travel due to COVID-19;

• employee quarantine or self-isolation due to COVID-19;

• employee refusal to work under Part II of the Canada Labour Code, R.S.C, 1985, c. L-2, (or equivalent law) due to COVID-19; and

• additional hygiene or passenger health screening processes put in place due to COVID-19.

Note that bolded part is mine. As Canada has issued a non-essential travel advisory for ALL international travel back on March 13, 2020, thus, any cancellations between Canada and the United States can be deemed an "uncontrollable" cancellation per CTA's guidance materials via this determination. Whether or not another airline is still operating between the same two city pairs is immaterial.