Does Canvas detect AI?
No
Canvas by itself does not. Canvas is a delivery platform, any AI score you see there comes from Turnitin or a similar tool plugged into it.
How it works
Canvas handles submission, grading and gradebook. Detection is an integration. If your institution has not licensed one, no AI score is produced at all.
The part people miss
Canvas does log submission timestamps and access events. That is activity data, not content analysis.
Flagged for something you wrote yourself?
There is a right order to handle it in, and editing the document first destroys your best evidence.