Early September would've worked for the Ontario by-elections as it would be far enough removed from the municipals.
Speaking of chain reactions, I think the most recent example of that was when Coderre resigned to run for mayor of Montreal. You had a by-election in Bourassa, then in neighbouring Viau (okay, no overlap, but caused by their MNA running in Bourassa) then the Montreal municipal election.
This stuff happens in the U. S. all the time. Most recently, John Kerrey was made SoS, so Rep. Ed Markey ran (and won) in the Senate special election, leading to a special in MA-05 (Markey's district), which was won by Katherine Clark, a state senator. Her seat in the state senate was won in a special election by Jason Lewis, a state representative, meaning there'll be another special election in a few months, for his state house seat.
