Row 30 is a bulkhead row, and is only seats D,E,F,G (the middle seats), there are no Row 30 A,C or H,K. Row 31 A,C/H,K are the seats at the exit door. The seat map on ac.com illustrates this if I haven't explained it well.
http://www.aircanada.com/en/about/fleet/seatmap/333.gif