Prime Minister Justin Trudeau said on Friday that Canada’s hospital system could be overwhelmed by a possible quadrupling of new Covid-19 cases by year-end as its biggest city Toronto prepared to impose a lockdown.

Trudeau implored Canadians to stay home as much as possible as a second wave of the novel coronavirus rips across the country, forcing several of the 10 provinces to reimpose curbs on movement and businesses. Cases continue to spike and authorities complain some people are being more careless about taking precautions...