• Leadership: Only Mr. Trudeau and Elizabeth May of the Green Party will be repeat performers from 2015 as party leaders. Several polls suggest that many voters still don’t know much about Andrew Scheer, the former speaker of the House of Commons who now leads the Conservatives.

Mr. Singh, a former Ontario provincial politician, also needs to define himself for a national audience. The wild card is Maxime Bernier, the libertarian former cabinet minister who has left the Conservatives to create the People’s Party of Canada.

• Money: Unlike in American elections, Canada’s laws make votes here comparatively low-budget affairs. But donations are still the fuel of campaigns. The last fund-raising reports from the parties show that the Conservative machine remains well oiled, pulling in 4.8 million Canadian dollars in the quarter ending in September. The Liberals raised 3.8 million dollars. Both of those results are relatively consistent with the recent past. But the New Democrats have fallen hard, with well under one million dollars over the same time period.

• Issues: Forecasting key election issues, like results, can be fraught. But unlike in 2015, Mr. Trudeau is unlikely to wander around the country making promise after promise. Many of his earlier vows remain unfulfilled or works in progress, and a handful were abandoned, notably a promise to reform how we elect members of Parliament. But he can point to a number of achievements, including middle-income tax cuts and the legalization of medically assisted deaths and recreational marijuana. And while Mr. Trudeau’s attempts to develop a relationship with President Trump came to a bitter end, a new Nafta was nevertheless struck.