In Ontario (as elsewhere), there's been a giant ramp up in cases since the start of September, with an accompanying discussion about whether or not reopening schools is the cause. But a recent testing blitz at a single Toronto school uncovered 26 infected individuals scattered across 18 classrooms:

https://www.theglobeandmail.com/canada/toronto/article-stude...

Still not obvious one way or the other about whether these students and staff are spreading it amongst themselves or if they all got it from other symptomatic cases in the community and independently brought it to school with them. But either way, it's sobering how much of it is going undetected.