Since May 2007, the Canada Elections Act provides for a general election to be held on a fixed date: the third Monday of October in the fourth calendar year following the previous general election. As the last election took place on September 20, 2021, the next fixed election date is October 20, 2025.
That said, the Canada Elections Act does not prevent a general election from being called at another date.
General elections are called when, on the advice of the Prime Minister, the Governor General dissolves Parliament. The Governor in Council (the Governor General, acting on the advice of Cabinet) sets the date of the election.
Section 57 of the Canada Elections Act specifies that the election period must last a minimum of 37 days and a maximum of 51 days.