Looks like sweeping changes on the renumbering of Europe flights. Appears they are numbered and sequentially grouped by destination and by departure time.
Examples:
800 YYZ-DUB (formerly 842)
836 YYZ-MUC (846)
852 YYZ-LHR (868)
854 YYZ-LHR (856)
856 YYZ-LHR (848)
858 YYZ-LHR (Unchanged)
872 YYZ-CDG (880)
824 YYZ-MAD (836)
820 YYZ-BCN (814)
896 YYZ-LHR (820)
880 YYZ-ZRH (878)
886 YYZ-VIE (898)
890 YYZ-FCO (Unchanged)
894 YYZ-MXP (Unchanged)
This will take some getting used to!