The functional reason that the US presidential election is so long is that the selection process for the candidate is tied to the election itself. The primary system requires extensive campaigning to seek the nomination, and that has to occur before the presidential election, in the same year.
That’s not how it works in a parliamentary system. The party leaders are chosen well in advance of the election, often years in advance.
Here’s the breakdown for the current Canadian party leaders, who will be leading their parties in the 2025 election:
Justin Trudeau - Liberal leader since 2013
Jagmeet Singh - NDP leader since 2017
Yves-François Blanchet - Bloc Québécois since 2019
Pierre Poilievre - Conservative leader since 2022
Elizabeth May - Green leader since 2022 (prior stint as leader, 2006 to 2019)
A second difference is that our party leaders are already in Parliament, and that’s where they’re campaigning, in the sense of setting out their positions and getting known to the country. We don’t have the period half a year before the election where we’re trying to get a handle on the potential leaders; we know who they are already, and by the rules of Parliament, if Parliament is sitting, as a general rule they have to be in the House, governmentin’. That cuts down on their availability for campaigning.
A third difference is that there is a formal legal beginning to the election period, which is absent in the US system: the dissolution of Parliament. Once the writ drops, dissolving Parliament, then the election is on. Technically, no-one is a candidate until that starts, because each one has to be nominated with Elections Canada to stand for election in their district, and that nomination process opens with the writ. They will normally have their party nomination sewn up for their riding in advance, but they’re not candidates for the House of Commons until after the writ drops and they file the necessary papers.
A fourth difference is that we don’t have primaries, which are a formal election process where the hopeful has to campaign and win the nomination, state-by-state. The primaries have to occur in the same year as the presidential election, but far enough in advance to allow for different primaries in different states. We don’t have that. Here, each party has their own system to nominate their candidates. There is federal regulation of the candidates’ election spending, but the system to get the party nomination is up to the party, and voting is restricted to members of the party. Those party nominations are done on a riding-by-riding basis, and generally don’t get much public attention.
The British system is similar. I’m not familiar with French elections, so can’t comment on that.