I wonder if it's the same one that was found in Hamilton back in April.
Yes, I was wondering the same thing. Observations from eBird in Ontario and vicinity:
Hamilton Mar 31-Apr 9
South of Buffalo, NY Apr 23-25
Point Pelee, May 13
Marie Curtis Park, Toronto, May 22
Sunnyside Beach, Toronto, Jun 25-Present
Indianapolis, IN Apr 12-19, Apr 28
Lafayette, IN, Apr 30
Indiana Dunes SP, IN, May 6
Clinton, NJ Mar 26-Jun 11
Montgomery County, MD May 9 - Jun 20
So it looks like 3-6 birds have been in the northeast this spring/summer. The one in New Jersey is overlapping with all other locations. The one in Hamilton/Buffalo could have moved on to either Maryland or Point Pelee/Toronto. Same with the Indiana bird, but more likely to Point Pelee/Toronto as it is closer than Maryland. So the one we see here in Toronto would be either the Hamilton bird, the Indiana bird or a different one. but I guess we never will know for sure.
/Thomas