Google’s founders have long fantasized about what would happen if the company could shape the real world as much as it has life on the internet.

“Years ago, we were sitting there thinking, Wouldn’t it be nice if you could take technical things that we know and apply them to cities?” Eric Schmidt, the executive chairman of Alphabet (now Google’s parent company), said Tuesday. “And our founders got really excited about this. We started talking about all of these things that we could do if someone would just give us a city and put us in charge.”

That is, of course, an outlandish idea. “For all sorts of good reasons, by the way, it doesn’t work that way,” Mr. Schmidt acknowledged. But there he was standing Tuesday before an array of Canadian flags, in front of Prime Minister Justin Trudeau and Ontario officials, to announce the closest thing anyone has seen to a tech company that takes the reins in a major city.

Toronto has about 800 acres of waterfront property awaiting redevelopment, a huge and prime stretch of land that amounts to one of the best opportunities in North America to rethink at scale how housing, streets and infrastructure are built. On Tuesday the government and the group overseeing the land announced that they were partnering with an Alphabet subsidiary, Sidewalk Labs, to develop the site.