Susan Lahey's appointment as the Progressive Conservative candidate in the York—Simcoe by-election, triggered by Caroline Mulroney's June 2026 resignation, anchors trader consensus at 97.6%. The riding delivered 59% PC support in the prior general election, and Lahey's background as an East Gwillimbury councillor provides local name recognition ahead of the September 3 vote. Active campaigning by PC figures and the party's organizational edge in this historically competitive district reinforce the implied probability. A late scandal, sharp drop in turnout, or unusually strong coordinated push by opposition parties such as the Liberals or NDP could narrow the margin, though the short campaign window and established voting patterns limit realistic paths for significant shifts.