Nice find. In eBird, there are no previous observations in York Region.
That's close to where I work but just couldn't get out in time. Nice find though! There were quite a few American Crows at Downsview yesterday so it looks like some big roosts have broken up and moved out. Maybe among the hundreds or thousands of American Crows were a few Fish Crows. I remember last year someone thought they saw (heard) Fish Crows on Bayview close to Steeles also in February.
You should submit this sighting to the OBRC. If it gets accepted, it will be put into eBird eventually.