Canadian Politics Today

The idea would be to have multi-family units of 1800-3000 square feet on top of each other, priced above condos but less than houses.

I think you just described the flats so popular in Montreal that have been around since the early 1900's. Most however are limited to 2-3 units tall, and either single or double wide (ie. 2-6 units in a building). The vast majority of buildings are in a row, but there are also many semi-attached and detached buildings as well. I would say they are smaller on average than what you are looking for. If you wanted to go higher, you would need more infrastructure like elevators, lobbies, and these days parking.