OTTAWA—The four opposition parties in Ottawa are making demands of the minority Liberal government ahead of next week’s federal budget, but their leverage is limited. NDP Leader Jagmeet Singh has pledged not to trigger an election regardless of what the budget has in store on April 19, a move that potentially weakens New Democrats’ say in the final product. “Our support for the actual budget is not probably a concern for the Liberals, because they want an election. They want an excuse to go to an election,” he said Tuesday. Singh is calling for a stronger federal role in on-the-ground COVID-19 vaccine administration as well as concrete steps toward a national child-care plan, which the Liberals have pledged periodically since 1993. Bloc Quebecois Leader Yves-Francois Blanchet says he would likely back the first budget in more than two years if it boosts monthly support for seniors and no-strings-attached health transfers …