I'll take the last comment first. There's no way a major international airport and agricultural future are on the same economic impact stage. A major international airport would generate far more jobs and economic impact.
The question is, would a Pickering project be successful? Pearson's latest master plan, released to the transport minister on December 1, 2017, says no. They are planning on accommodating all the aviation needs at Pearson before they have to add the sixth runway in the next 20 years. They say they have plenty of capacity, and they're working in the southern Ontario airports network of 10 other small airports, including Oshawa, to accommodate the aviation growth they forecast in the foreseeable future. That network right now is planning to handle Ontario's aviation capacity for the next 30 years.