OTTAWA—The federal Liberal government is promising cash-strapped cities billions of dollars in permanent funding for their public-transit systems—though most of the money won’t start flowing until later in the decade. Prime Minister Justin Trudeau made the $14.9-billion announcement Wednesday as he prepared for a virtual meeting with the mayors of Canada’s largest cities, many of them struggling to make ends meet due to the COVID-19 pandemic. “These investments will support major public transit projects like subway extensions, help electrify fleets with zero-emission vehicles,” Trudeau said during a virtual news conference. “They will also be used to meet the growing demand for walkways and paths for cycling and help rural and remote communities deliver projects to meet their mobility challenges.” About $6 billion will be available to municipalities right away for projects that are ready to go, according to the government, while the remainder will go into a $3-billion per year …