In Toronto, it's the proliferation of "lot-split specials" - new single-detached homes, often created through the splitting of a smaller dwelling on a larger lot into two new lots. Results in a narrow frontage, typically with a flat-roofed, 2.5-3 storey house with a single car garage. The flat roof lets them max out the zoning envelope.
You can find these literally all over the city:
Typically sell for between $1.3 and $2 million USD depending on size, location, age, and level of finish.