My megaproject ideas are mostly pretty standard. I'd build a high speed rail network across North America, and build and expand metro and regional rail systems in and around every city. I'd turn all cities and suburbs into fifteen-minute cities. I'd decommodify housing, and build ten million units of public/social/non-market housing, mostly three bedroom units. I'd link those last three policies together by building TODs around the new Metro and rail stops. And I'd build bicycle networks in every town and city and connect them to the TODs. I'd build bridges and walkways across skyscrapers. I'd put a bidet in every American toilet (uses less water than toilet paper apart from being more comfortable). Fiber internet in every home. A heat pump in every home. An induction stove in every kitchen. Phase out fossil fuels and power everything with Pumped Storage Hydropower and Geothermal. I'd make the US go Metric.
But my truly crazy, obsessive idea would be to bring back the French Revolutionary calendar. Or I'd purge all French influences from English.
High speed rail running the 'spine' of the americas - people should be able to go from Alaska to the far end of Chille and not need to transfer (although one imagines a number of stops along the way)
obviously, this would also be paired with a lot more freight rail, with the goal of eliminating as much intra-americas cargo voyages as possible. Really, that would be the true aim of the project, but the high-speed passenger line would be the forward face of it.
Run some ultrahigh voltage DC power lines with it and have a hemisphere wide electric grid