Question

why is canada a multicultural country？

Answer 1

Canada has a diverse makeup of nationalities and cultures and constitutional protection for policies that promote multiculturalism rather than a single national myth.

Historically Canada has been influenced by British, French, and aboriginal cultures and traditions. Many North American Indigenous words, inventions and games have become an everyday part of Canadian language and use. Through their culture, languages, art and music, aboriginals continue to exert influence on the Canadian identity.

以下作文，先说历史
when we talk about the multiculturalism of canada, the first priority should be given to the history of the country.
The land that is now Canada was inhabited for millennia by various groups of Aboriginal peoples. Beginning in the late 15th century, British and French expeditions explored, and later settled, along the Atlantic coast. France ceded nearly all of its colonies in North America in 1763 after the Seven Years' War. In 1867, with the union of three British North American colonies through Confederation, Canada was formed as a federal dominion of four provinces. This began an accretion of provinces and territories and a process of increasing autonomy from the United Kingdom.
Europeans first arrived when Norse sailors settled briefly at L'Anse aux Meadows in Newfoundland around 1000. No further European exploration occurred until 1497, when Italian seafarer Giovanni Caboto (John Cabot) explored Canada's Atlantic coast for England. The English established fishing outposts in Newfoundland around 1610 and established the Thirteen Colonies to the south. To avert conflict in Quebec, the British passed the Quebec Act of 1774, expanding Quebec's territory to the Great Lakes and Ohio Valley. It re-established the French language, Catholic faith, and French civil law there. This angered many residents of the Thirteen Colonies and helped to fuel the American Revolution. The Treaty of Paris (1783) recognized American independence and ceded territories south of the Great Lakes to the United States. Around 50,000 United Empire Loyalists fled the United States to Canada. To accommodate English-speaking Loyalists in Quebec, the Constitutional Act of 1791 divided the province into French-speaking Lower Canada (later the province of Quebec) and English-speaking Upper Canada (later Ontario), granting each its own elected Legislative Assembly.
然后说现在
In Quebec, cultural identity is strong, and many French-speaking commentators speak of a Quebec culture as distinguished from English Canadian culture, however as a whole Canada is a cultural mosaic — collection of several regional, aboriginal, and ethnic subcultures. It is often asserted that Canadian Government policies such as publicly-funded health care, higher taxation to distribute wealth, outlawing capital punishment, strong efforts to eliminate poverty, an emphasis on multiculturalism, imposing strict gun control, leniency in regard to drug use and most recently legalizing same-sex marriage are social indicators of how Canada's political and cultural evolution differ from that of the United States.
Many Canadians value multiculturalism and see Canada as being inherently multicultural. However, the country's culture has been heavily influenced by American culture because of its proximity and the high rate of migration between the two countries. The great majority of English-speaking immigrants to Canada between 1755 and 1815 were Americans from the Thirteen Colonies; during and immediately after the American Revolutionary War, 46,000 Americans loyal to the British crown came to Canada. Between 1785 and 1812, more Americans emigrated to Canada in response to promises of land.
这里举个例子

再说自己感受里的各种文化
the history of canada's muticulturalism can only give us a glancing picture of its culture prosperity and diversity. nevertheless, when it comes to me, it'll remind me of popular media and visual art, digital art, music, sports and the life style of course. Take music for instance, the Canadian music industry has developed a music infrastructure, that includes church halls, chamber halls, conservatories, academies, performing arts centres, record companies, radio stations, and television music video channels. The Canadian music industry has produced internationally renowned composers, musicians and ensembles. To speak the truth, i'm always titling myself "a big fan of Celine Dion, who is born and grew up in Canada but a fluent speaker of French and English. Her excellent works of art are kind of a reflection of the country's muliculturalism. I bet you will fall in love with them if you'd try!

Answer 2

主要还是殖民导致的，你可以参考：http://baike.baidu.com/view/3647.htm#2

Answer 3

At least we know there are two official languages in Canada, namely English and French, which means this country has come under the influence of both English and French cultures, and as a result, we can say it is a multicultural country.