A
history of the Philly-area main line which I think the OP was referring to.
My understanding is that this basically refers to suburban towns built along rail lines stemming from large northeastern metro areas in the U.S. Predating the car, they have solid walkable main streets and small CBDs themselves, and tend to have larger more palatial houses. In the NYC area you've got all of the towns between the Hudson River and Long Island Sound, north of the city proper, stretching up into Connecticut.
I don't know about the history of rail access, but some of the suburbs on Montreal's west island seem to fit the bill: Pointe Claire, Baie d'Urfe, etc.
As Someone123 mentioned, the Halifax metro region has some of this too, akin to a micro version of what you see in the Boston metro region. They tend to wrap around the Bedford Basin and extend north. Bedford would be the most developed. Places like Fall River and Windsor Junction might fall into this too, but because of much slower growth they don't really have much in the way of commercial cores or anything like that, and feel much more rural. Some large estates and stuff out that way though.
You can see a tiny bit of this in Saint John, NB, too, in communities along the rail line, like Rothesay and Quispamsis, where you've got these historic little junctions and turn-of-the-century subdivisions, Cape Cod-looking streets.