In Canada, the celebration of Victoria Day occurs every year on Monday, prior to May 25th. It is the official celebration in Canada of the birthdays of Queen Victoria and Queen Elizabeth II. Victoria Day was established as a holiday in Canada West (Now Ontario) in 1845, and became a national holiday in 1901. Before Victoria Day became a national Holiday, people had celebrated Empire Day , beginning in the 1890s as Victoria approached her Diamond jubilee in 1897.
Victoria, queen of the United Kingdom of Great Britain and Ireland and empress of India was born on 24 May 1819. She ascended the throne after the death of her uncle George IV in 1837 when she was only 18. She ruled until her death in 1901 when her son Edward the VII became king of England.

The Sovereign's birthday has been celebrated in Canada since the reign of Queen Victoria (1837-1901).
May 24, Queen Victoria's birthday, was declared a holiday by the Legislature of the Province of Canada in 1845.

After Confederation, the Queen's birthday was celebrated every year on May 24 unless that date was a Sunday, in which case a proclamation was issued providing for the celebration on May 25.

After the death of Queen Victoria in 1901, an Act was passed by the Parliament of Canada establishing a legal holiday on May 24 in each year (or May 25 if May 24 fell on a Sunday) under the name Victoria Day.

The birthday of King Edward VII, who was born on November 9, was by yearly proclamation during his reign (1901-1910) celebrated on Victoria Day.

It was not an innovation to celebrate the birthday of the reigning sovereign on the anniversary of the birth of a predecessor. In Great Britain, the birthdays of George IV (1820-1830) and William IV (1830-1837) were celebrated on June 4, birthday of George III (1760-1820).

The birthday of King George V, who reigned from 1910 to 1935, was celebrated on the actual date, June 3 or, when that was a Sunday, by proclamation on June 4.

The one birthday of King Edward VIII, who reigned in 1936, was also celebrated on the actual date, June 23.

King George VI's birthday, which fell on December 14, was officially celebrated in the United Kingdom on a Thursday early in June. Up to 1947 Canada proclaimed the same day but in 1948 and further years settled on the Monday of the week in which the United Kingdom celebration took place. George VI reigned from 1936 to 1952.

The first birthday of Queen Elizabeth II, in 1952, was also celebrated in June.

Meanwhile, Canada continued to observe Victoria Day. An amendment to the Statutes of Canada in 1952 established the celebration of Victoria Day on the Monday preceding May 25.

From 1953 to 1956, the Queen's birthday was celebrated in Canada on Victoria Day, by proclamation of the Governor General, with Her Majesty's approval. In 1957, Victoria Day was permanently appointed as the Queen's birthday in Canada. In the United Kingdom, the Queen's birthday is celebrated in June.

from http://www.inglewoodcarecentre.com/history/victoria.htm