Trudeau, 49, called the vote two years early to seek public approval for his left-of-center government's handling of the COVID-19 pandemic and regain the majority in Parliament that he lost in 2019. He first took power in 2015.
His initial healthy lead vanished amid voter unhappiness with the early call. Polls show that neither the Liberals nor their rival right-leaning Conservatives have anywhere near the 38 percent public support needed for a majority.
Trudeau, whose government racked up record levels of debt to tackle the pandemic, intends to fly from one end of the country to the other on Sunday, covering some 2,800 miles (4,500 km), in a last-minute bid to rustle up votes.
"We now get to pick the right direction for our country to keep moving forward, or to let Conservatives take us back," Trudeau told a crowd of around 200 volunteers at his first event of the day in Montreal.
In contrast, Conservative leader Erin O'Toole planned to spend the entire day in parliamentary constituencies near Toronto, Canada's largest city and pivotal for any party seeking to win power.
O'Toole, 48, initially took a lead after hammering Trudeau over what he called an unnecessary a power grab during the fourth wave of COVID-19. But in recent days he has been on the defensive over his opposition to the idea of vaccine mandates.
"We do not need a Conservative government that won't be able to show the leadership on vaccinations and on science that we need to end this," Trudeau told reporters in Montreal.
A senior Liberal campaign official said Trudeau brought momentum going into the final weekend. A string of opinion polls in the final days show the Liberals and Conservatives tied at around 32 percent.
This favours the Liberals, whose support is focused in large urban centres rich with constituencies. The Conservatives' support base is in more sparsely populated rural regions and the west of the country.
If Trudeau does come back with another minority, he would most likely depend once again on the left-leaning New Democrats of Jagmeet Singh, who want higher levels of spending.