Opposition parties have said they expect Morneau to provide a road map for reshaping emergency aid measures that are set to expire in the fall and keeping spending and deficits under control.
Direct federal support to individuals and businesses will total $212 billion this year, driving spending levels to their highest since 1945.
Fuelling the deficit is also an unprecedented drop in economic output and employment that will cut revenues the government expected to receive this year.
"Our government took on debt to reduce the amount Canadians themselves had to take on", he said.
Due to the COVID-19 spending, the Canadian government now projects its debt-to-GDP ratio will rise to 49.1 percent in 2020-21. The yield on benchmark 30-year debt increased 10.8 basis points to 1.092 per cent, according to Bloomberg data, as investors reacted to the forthcoming flood of paper.
While the announced deficit was larger than anticipated - most economists expected a deficit of just over $250 billion - the government of Liberal Prime Minister Justin Trudeau is justifying the budget shortfall as the lesser of two evils.
His government spent so Canadians wouldn't have to take on more debt, Trudeau says, and four months later the country has slowed the spread of the virus and certain sectors of the economy can reopen.
Canadian Chamber of Commerce's president and CEO, Perrin Beatty, said the deficit and added debt, which is worth almost half the country's GDP, will "undermine Canada's fiscal capacity for decades".
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Morneau, the first finance minister to oversee a credit rating downgrade in 25 years, is under pressure to provide at least cursory assurances the government will return to a more fiscally prudent path once the coronavirus crisis has passed.
"Some will criticize us on the cost of action", Morneau said in a speech in the House of Commons on Wednesday.
At the time, Canada's debt-to-GDP was at about 66% - the highest in the G7 - and interest rates were high.
NDP Finance Critic Peter Julian said he wants to see programs expanded and the wealthy taxed to pay for it, "So that we can preserve and enhance services that all Canadians need".
Morneau said while some will criticize the government on the cost of these measures, the size of the deficit is more of a testament of the impact the pandemic had on the economy.
In a statement, the Government says, "Canada's COVID-19 Economic Response Plan is ensuring Canadians have the support they need to put food on the table and keep a roof over their head".
Adding to the deficit is a $37.3 billion boost to the federal wage subsidy program, signalling an expansion and incoming changes to the benefit.