There is a new instruction given from New York ISO to the IESO recently.
When demand in New York is forecasted to be less than 27,000MW exports to New York are at full 1450MW (unless there are outages).
When New York demand is expected to peak between 27,000 – 30,000 exports to New York will be limited to 1150MW.
If demand in New York is expected to peak above 30,000 exports will be further limited below 1150MW.
UPDATE: June 14 2017 at noon
Further to the instructions listed above when demand in New York is forecasted to be above 33,000MW exports to New York will be limited to 500MW