Like many countries, Canada has spent heavily to support individuals and businesses hard-hit by the lockdown measures.
Since the mid-1990s, successive federal governments sought to avoid running up large deficits, and promised to return to balanced budgets if they did, for example after the 2008 global financial crisis.
The Liberals began to shift away from that under Mr Trudeau, who campaigned in 2015 on running modest deficits to invest in things like infrastructure and a new child benefit programme.
Mr Trudeau needs to add at least 15 seats to the Liberal bench to clinch a majority government.
In 2019, the Liberals fell short, leading to a minority, or hung parliament, and Mr Trudeau has had to rely on the support of opposition parties to pass legislation.
In Canada, a minority government is typically, but not necessarily, formed by the party that has the most seats.