The way land use planning works in Ontario is that areas have to be within the "urban boundary" in order to be developed for residential or industrial uses. The province requires municipalities to have a certain amount of lands within their boundary to accommodate growth for 30 years (just upped by the conservative government to 30 from 20).
Every 10 years or so municipalities review their urban boundary, look at how existing growth areas have been absorbed, population projections, intensification rates, etc. and determine if they need to add more land.
In this case, Hamilton is identified as growing from about 570,000 people today to over 830,000 in 2051 and had to decide how to accomodate that.
The planners at the City recommended accomodating 60% of it through intensification, and the remaining 40% through new suburbs. Growth in Hamilton over the last decade has been about 25% through intensification and 75% through new suburbs, so this is a substantial change.
There was a big grassroots movement from environmentalists to not expand the urban boundary and instead accommodate the 250,000 people moving to the city over the next 30 years solely through intensification.
This has regional planning implications as it will result in a huge shortage of single family homes in the market, and will likely result in growth getting pushed to other, adjacent municipalities in Brant County and Niagara. If the no-expansion-option stands, it is likely that Hamilton will fall short of it's population projections as the market will shift growth to other areas that can provide the desired product type.
The province warned the City that it would over-rule it if it implemented the no-urban-boundary-expansion option, and is likely do so now. The no-urban-boundary-expansion option clearly violates provincial planning policy which requires land to be set aside based on population projections and market demand.
I'm not sure if I'd even characterize modern Southern Ontario new suburb areas as "sprawl" anyway. The minimum densities are so high that SFDs typically account for only about 1/4 of new units in the areas, with most coming through townhouse developments and apartment buildings. They are actually very, very dense. The SFDs that do get built are on tiny lots, often smaller than inner city Toronto lots.
The new areas in North Oakville show the kinds of densities required pretty well - it's a very dense form of development.
Hamilton is also already experiencing a huge building boom in it's core, where they recently implemented as of right development of 30 storey buildings across most of the downtown. By my count there are around 40 buildings over 20 storeys proposed and under construction in the downtown right now.