The big fight will be in the land valuation for the expropriation. They are currently trying to rezone the land to make it more valuable - they have no intention of building the ORCA proposal. It's a play to make the land look valuable. I am doubtful however - the cost of decking the corridor to make the land developable would cancel out almost any value derived from its development potential. I'm seriously doubtful the ORCA proposal works from a financial perspective even if land costs = $0.
If that is the case, the city likely won't have to pay much. But you can sure bet that the ORCA will certainly try to make it out that this land is worth a ton of money and is a huge development site just waiting to happen, even if it isn't.
The fight is going to be in the appeal process for the expropriation. The city will issue the notice, take control of the land, and the purchase price can be appealed to the courts afterwards. This court battle happens relatively quickly, but I wouldn't give ORCA great chances, either.
The point is that we aren't going to see some epic fight here where the city struggles to take control of the land. The city will take control of the land even if ORCA protests - and the park can be built as they fight it out in court.
One of the biggest differences in expropriation law between Canada and the US is that in Canada the government takes control of the land regardless of if there is an appeal. South of the border, the appeals must be resolved before land is handed over. This is being seen for the new Detroit Windsor bridge currently - the canadian land has been under government ownership for years, while they are still fighting legal battles for ownership of land on the US side.
Spadina and Bathurst are so close together that it is likely one stop with two entrances. GO platforms are over 300m long remember, with only 600m between the two streets.