That can be impossible when there is nothing planned for the site when the initial purchase is being made, so don't jump to a conclusion that the buyer is at fault.
Given the record number of lots being development in Toronto, that's at the buyer's risk.
Yes, when the Brant Park condos started construction (around summer 2013), there was no application for 51 Camden (until August 2015) so the initial precon buyers would have no idea but let's look at Google Streetview:
When you see those raggedy buildings right beside the site to the north and it doesn't raise questions to the buyers on the north side that perhaps that site may get developed in the future, especially after you, yourself bought into a project were similar raggedy buildings were standing, then you better believe it that it's the buyer's fault if they're not OK with it.
It's the buyer's duly responsibility to do their due diligence to the fullest extent possible AND also understand that there are always risks involved. We have so much information available at our disposal these days that there's no excuse.
I'm sure those northern units were cheaper than the south-facing Adelaide ones, and even more so if they were facing west onto the park on Brant.
In any case, the people complained (as the only thing people know how to do these days), they lost and now 51 Camden is approved to be redeveloped. Tough luck & suck it up; there are worse things in life.
I feel more sorry for the units in the building just down the street, circled in yellow. They're staring straight at a cement wall. Here's a closer look before anyone jumps on me and telling me there are no windows: