I don't think the cancellation was commemorating anything in particular, other than the sender of the postcard was likely a passenger on the ship and the cancellation merely reflects the date the postcard was mailed (presumably from the ship). However, it may be reflecting one of the last cruises on the ship from Le Havre to Montreal that began in 1957 and, according to the history below, must have ceased on or before 1963 (when it was used for cruising only).
Here's a brief history on the ship:
The Homeric was originally the Mariposa. She was a 18,017 gross ton ship, length 632 feet x beam 79.4 feet, two funnels, two masts, twin screw, speed 22 knots.
Accommodation for 475 first class and 229 cabin class passengers. Built by the Bethlehem Shipbuilding Corporation, Quincy, she was launched for the Matson Navigation Company in Los Angeles on 18th July 1931. The Mariposa was used on the San Francisco – Honolulu – Sydney service and in 1941 entered service as a US Navy transport.
After wartime service, the Mariposa was laid up at Alameda in 1946 and in 1953 was sold to Home Lines, Panama and renamed the SS Homeric the following year.
The Homeric was completely refitted with accommodation for 147 first class and 1,096 tourist class passengers. The Homeric started regularly scheduled Southampton – New York sailings in 1955 and Le Havre – Montreal sailings in 1957.
From 1963 she was used for cruising only and after a serious fire in 1973, it was found uneconomical to repair her and she was sold for scrapping at Taiwan.