A friend associated with the local hospital system sent me this, in response to the graphs I posted here.
There have been zero reported cases to date of laboratory-confirmed influenza since Aug 30th, 2020 in London [Ontario]. For comparison, last year for the same period there were a total of 105 cases (75 influenza A and 30 influenza B) in London.LHSC routinely tests for influenza and other respiratory viruses when testing for SARS CoV-2, at least since November 2020. Therefore, the decrease in people testing positive for influenza seems real.
My take: if the cases of flu are not being mis-represented as covid-19, the most likely explanation for the decline in flu cases is that people are being more careful this year: washing their hands more, using hand sanitizer, wearing masks, avoiding crowds, etc. But of course I'm open to other explanations.
Update: Jack suggests that more people have gotten the flu shot this year and have gotten it earlier. That could also contribute to the decline in flu cases.