It didn't appear that Pearson was doing anything different when I went through this past weekend (also flew AA). They've added a question about China/Iran to the Passport Control kiosk, but that seemed to be about it.
I was questioned quite intently by the CBSA Officer, though I don't think this had to do with COVID-19. He seemed suspicious about why someone would travel from the west coast to Toronto for a day and a half, in winter. Apparently "because it was a cheap fare" was not a good enough reason.