Funny fact about those...
There was one intensive day where military planes at least 20 thousand feet up made a checkerboard pattern over the whole city (like 100 km radius) it was huge and very visible, many people were talking about it...
I asked a friend of mine who works in a healthfood store and he said lets call health canada, they'll tell us whats going on.
They said it was probably an insecticide used to combat ticks in the city, that they were spraying the whole region for the tourist intensive season.
Then he asked what was the insecticide, and if it had been tested for toxicity ; they said :
Oh of course sir its a military based operation, so I'm certain they have made all the necessary procedures to insure safety. But you will have to call them to have anymore information, and I doubt they will be willing to talk without an official inquiry.
We both went like... what the ?! They usually say it dosen't exist and we're hallucinating, that they are just condensation clouds. (even if I never seen a condensation cloud last more than 5-10 mins.
Anyways... the military would not comment about it... they said it was condensation trails from flying exercises. When asked about the checkerboard pattern, they hung up.