I'm going to play off of some things other people have been saying. Let's suppose that after the Treaty of Paris was signed in 1783, it became the catalyst for a Maritime Union under the name Nova Scotia (since the whole region had been called Nova Scotia at different points before 1783)
The Province of Nova Scotia - Capital Halifax
The Province of New Brunswick - Capital Fredericton
The Province of Prince Edward Island - Charlottetown
The Province of Cape Breton Island - Capital Sydney
So the foundations of a union between the new provinces are put into place and in 1814, after the end of the War of 1812, the 4 provinces unite to form the Federation of Nova Scotia. The province of Nova Scotia becomes the Province of Acadia with the Capital moving to Truro. The new federal capital would be in Halifax.
Due to being their own nation, they have their own currency. Today they would have 5 major banks; BrunswickBank, Farmers Bank, Scotiabank, Union Bank, and Merchants Bank. They were all located in Halifax with the exception of BrunswickBank being located in Saint John and Farmers Bank being located in Charlottetown.
Let's assume that military bases were still built in WWII. Today they would exist in Chatham (Airforce & Military), Greenwood (Airforce), Halifax (Navy & Military), Summerside (Airforce, Navy).
Chatham would have a small amount of Air Force units but be the primary location of what is now CFB Gagetown. Greenwood would basically be as is. Maybe slightly smaller. Halifax would basically be as is, Sheerwater wouldn't exist. Summerside would have a Navy unit next to the Air Force base, as it is right on the water. This would allow for patrolling of the Gulf of St. Lawrence while the Navy base in Halifax would patrol the Atlantic.
In place of NB Power, NS Power & Maritime Electric would have been a new crown corporation called Nova Scotia Electric. Let's assume all of the same generating facilities still get built. Let's also assume that the Macquac Dam is built properly and that they don't need to replace it so early.
Saint John's economy is still very much industrial based, but it is a bit diversified. For starts, by the time the Irving refinery is built, that area had already been developed. There is a bridge from St. John St. to Broad Street and then from Broad St. to Bayside Dr. Most of the Cities industrial ports were built in the Red Head/Anthonys Cove area. The Irving refinery and Pulp Mill and Paper Mil all end up getting built in the Lorneville area near the Coulson Cover Generating Station. The Lancaster side of the harbour becomes more modern. There is a very good subway system serving Lancaster, uptown and the core area of Saint John. A light commuter rail system is also built to help connect the suburbs. There is giant office towers for Irving Oil, JDI, and NBTel on the Lancaster side. The population of Greater Saint John at this point would be around 1.2 Million, with around 300,000 living in Lancaster, which as almost been completely rebuilt. Uptown Saint John has around 200,000 living there, largely in upscale condo buildings built along the waterfront. The Saint John Regional Hospital and UNBSJ remain where they are today. However, UNBSJ becomes its own medical school, The University of Saint John, it has a much bigger campus as well.
The highway through the city has never been built, instead a northern by bypass is built from Dury Cove, north of Rockwood Park before going south, through Milledgeville and crossing the Saint John River in the Milford area. Instead of the route used on the Moncton-Fredericton Route 2 highway, a new route would continue west from Sussex, south of Bellisle Creek, before crossing the Saint John River in Hampstead. From there it would continue north to the village of Gagetown before heading west to Fredericton. To replace the route 7 highway to Fredericton, a highway would be built from Milledgeville north crossing the river to Summerville, before crossing the river again, connecting to the new Route 2 highway. The 119 through Quispamsis would also connect to this highway via another bridge.
Oromocto essentially wouldn't exist due to the military base being in Chatham instead. This would increase the population of the city by around 9000 people. This would be a big boost to the Miramichi area. The proposed northern bypass of the city would be built. Route 8 from Fredericton to Miramichi would be 4 lanes. Route 11 from Miramichi to Moncton would be four lanes as well. The population would be around 50,000.
Greater Moncton now has a population of around 1.3 Million. It is a hub for high tech industry jobs, call centres, insurance, and telecommunications. It has multiple head office towers of software companies, telecommunications companies, and insurance companies. Moncton is a very clean city, with lots of parks, and a well planned out subway system, with lines going through Dieppe, to the airport, up Moutain Road to the Trinity Drive retail hub etc. There would also be two high end shopping malls, the Shops at Champlain and Highfield Square. The NHL also has a team in Moncton that plays in an arena located at the Highfield Square Complex, which is a 3 story shopping complex, with an IMAX theatre, convention centre, and a 17,500 seat arena. The city also has a very big tourism sector. The so-called Magnetic Hill strip has 4 Casinos, 3 amusement parks, 20 hotels, and a golf course, not to mention the actual magnetic hill attraction. There is multiple new river crossings, including Wheeler Blvd, Bridgedale Blvd. and Lower Coverdale. The Petitcodiac Causeway was never built, however, a bridge was built alongside the power transmission lines that also cross the river nearby. Before the big expansion of the George Dumont hospital in the 1970's the hospital was actually relocated to what would be the site of NBCC, in Dieppe. Here a massive hospital campus was constructed in the french city of Dieppe. In the 1950's the CN shops in Moncton were removed due to the lack of usable space in the city itself. The site on the corner of Vaughan Harvey Blvd. & Millennium Blvd. would become the site of the future Moncton Hospital. The biggest hospital campus outside of the Halifax area.
Summerside is another city that would benefit from the increased military presence. The population would be around 70,000. Summerside would also benefit from the increased cost of living in Charlottetown. There would be 1 four-lane highway between the two cities, with a connection to the confederation bridge, which would have been built in the 1970s or 1980s as a four-lane bridge connecting PEI to NB. Charlottetown's population at this point would be around 375,000 with Stratford having around 90,000 and Cornwall having filled in its rural area, now having reached 110,000.
Halifax's population has reached 2 Million people. It has a huge financial district. The NHL has a team play in the 18300 seat Union Bank Forum, built on the site of the former Cogswell interchange. There is an extensive subway system and an above-ground commuter rail system to help make the transit in the city more efficient. There is 4 new crossings, one being an 8 lane tunnel from Dartmouth to downtown, the other being a 6 lane tunnel to replace the MacDonald Bridge. The other 2 are two different crossings of the Northwest Arm. Highway 113 has finally been completed, as well as the Burnside Connector highway. There is also an 8 lane highway from Halifax all the way to the provincial capital in Truro, which now has a population of around 75,000.
This was a lot of fun. What are people's thoughts on some of my ideas?