Just wondering about such a large flight status discrepancy.

My brother is aboard AC 32 into YYZ tonight. Air Canada shows the flight on time (actually, arriving 9 minutes early), as does the GTAA Web site. However, other sources, including Flightstats and a number of others, are showing the flight scheduled to arrive ~ 4 hours late. So there's a 4 hour estimated arrival time difference. All of these sources seem to agree on the departure time.

Just wondering how this could be possible. A few minutes apart, I could understand. But that much of a difference seems very strange to me.
Also, I would assume AC has the most accurate status. Is there any reason to believe flightstats would be more accurate than AC itself?