Slightly different perspective:
A lot of people have put forward cogent arguments how circumstances were different when applications were canceled in the past and won't/can't happen now. Common arguments are:
-Files were paper based, system needed to change.
-Economy of Canada was changing and no longer needed certain NOCs.
If you look at present situation, those reasons are somewhat applicable even today:
-Canada wants to target certain NOCs now (Hint: new immigration system that is expected to be announced soon) and perhaps the long list of Apps already in post AOR have NOCs which are not relevant to the current labor market.
-Second, Canadian labor market has suffered enormous job loses due to businesses closures during pandemic which has changed the economic landscape and needs of Canada. Therefore, enormous amount of people in the backlog (mostly FSWs) are no longer needed at present time since there aren't that many job available.
Conclusion: If Canada wants to cancel Apps in backlog, they can, same circumstances are present as they were in the past when Apps were canceled.