Under a proposal announced last week, the city wants to preserve half of a 365-hectare undeveloped swath of land as part of the l'Anse-à-l'Orme green space and allow the rest to be developed.
Montreal Mayor Denis Coderre has said the project could include upwards of 5,500 new homes, along with new schools, office space and parks.
There are concerns, however, because one property owner is holding on to part of the green space.
Russell Copeman, the Montreal city councillor responsible for urban planning, said the land in question will stay green.
"We do not need to buy the land to have it protected," Copeman said Monday.
"It is within the ecoterritory, and there will be no development on the land."
Copeman said the city stopped negotiating with the landowner four years ago because they wanted too much money.
The city could have expropriated it but decided against it.
"Courts and tribunals that deal with expropriation, generally speaking, tend to award higher amounts than the market value when you expropriate," he said.
"So we use expropriation with great discernment."
Project will increase traffic woes, opposition says
Luc Ferrandez, head of Projet Montréal, says Copeman has handled the situation poorly and should have taken action sooner.
"He is the head of the urbanism. He should have controlled this before," Ferrandez said.
Projet Montréal is against the development project, arguing it would destroy a rare green space and contribute to suburban traffic woes.
"With this, you're just going to add 10,000 cars on the [Highway] 40," Ferrandez said.
"It's inevitable, because it's far away and the only means to get around will be to use their car."
Save l'Anse a l'Orme, a local conservation group, is also concerned the project will destroy an area of rare biodiversity.
The group has started an online petition against the project. The petition argues that "natural areas in proximity to urban centres play a very important role as buffer zones and deserve to be preserved."