This variation might be vernacular, but it's an adaptation of the Second Empire style for modest housing of the time. Unlike Bay and Gables, there aren't enough of these houses to forge a unique style.
These little second empire rowhouses aren't that uncommon actually, although the brick is often painted over, which might make those less noticeable. I actually found some
in Markham that look very similar.
These rowhomes in Trinity Bellwoods would be an example of these Second Empire homes that were alterred a fair bit. 133,135 and 137 look like they might have been built the same way, but seem to have been modified beyond recognition.
These are somewhat strange, but they possibly represent a sort of transition between Victorian and Craftsman and Edwardian styles.
They are pretty common though. They might have look like
these on Queen East originally.
These look like Craftsman houses, common in North America in the early 20th century. Many in Toronto are bland, though it might be because of renovations over the decades. Bloor West Village has some beautifully restored examples, for instance on Kennedy Avenue just north of Runnymede Station.
Looks like you're right, there are similar homes in other American cities, although they all seem to be detached (not semis). Do you think the Toronto ones might have originally been detached too, or did Toronto always have more semi-detached homes than American cities?
Anyways, there is one style of housing that is extremely common in Toronto and I've yet to see in other regions, which are homes like
these semis in the Jane-Finch area. They seem to have been built all over the suburbs in the 60s, especially in the North-East 416 suburbs, but also in parts of Scarborough, Western North York, Mississauga and Brampton. They were built in a very specific way, with two single-car garages adjacent to each other. The driveway is a bit wider (on each side) than the two single car garages. Much of the building is inset, with the inset being the width of the driveway and including the garages, two balconies above them and usually a door on either side of the garage. There would usually be a wall partitioning the inset, and a large window onto the balconies above each garage, with a door to access the balcony on either side. The main entrance to the house would be raised usually halfway between the garage level and balcony, on either side of the house and be the only part of the house that's not inset. The rear of the house is sometimes raised so that it is two floors high facing the back yard. The semi-detached homes sometimes have their own hip roof, sometimes a shared hip roof.
I haven't seen any homes like these in American cities.