OTTAWA — Canada’s two main political party leaders won’t boast about the connection, but they have at least one important thing in common these days: As a new session of Parliament opens Monday, they’re both sitting on hot seats. Facing upcoming periods that may well determine their political fates, Prime Minister Mark Carney and Conservative Leader Pierre Poilievre are both approaching hurdles they need to get over in the coming weeks and months to ensure their grips on power. The Liberals are still polling at about the same level as they were during last year’s election, with...