It's a tricky business. We have 13 jurisdictions in Canada besides the federal government, and they all hold elections. There are municipal elections as well. Within each jurisdiction you can have two sets of elections, so there could be 26 different elections.
That being said, it's impossible to make sure that whenever the federal government sets or calls its election, there is no election in any one of the jurisdictions that make up this country. In 1988, I remember that there was a provincial byelection in my area and a municipal election, and the federal election was piled on at the same time. People were looking at signs for three different levels of government. They were challenged, but people managed to get through that and sort it out.
Monsieur Proulx has indicated that not all of them choose Monday, which happens to be the day of the federal election. He indicated that the date is sometimes on a Sunday in provincial elections. I know that Ontario likes to go on a Thursday.
It seems to me that once having set the federal election date, other jurisdictions might not want to have their elections coincide exactly with when they know the federal election is going to take place. It's impossible to guarantee there will never be any overlap between us and the other 26 jurisdictions that could be holding elections.