The Canadian federal government requires bilingualism in a number of institutions, including some (not all) federal government posts. The reason is historical, but still relevant today.
Parts of Canada were first colonized during the 16th century by French people. During the 17th century, the British established many colonies further south and took increasing interest in territories to the north. The French and the British fought a number of wars, and eventually, with the treaty of Paris in 1763, the French no longer controlled any part of what is now known as Canada: it was a British colony.
At the time, French speakers made up the majority of the population of Canada: approximately 30,000 English speakers in 1791 vs 140,000 French speakers (and that's after many Loyalists fled from colonies that had revolted against and become independent from the British empire; I can't seem to find estimates for 1763). (Also, about 80,000 natives.) The British had the upper hand militarily and the French government wasn't very interested in North America, but the French speakers in Canada had little reason to be loyal to the British government, their historical enemy. The British wanted to assimilate the French speakers, notably through the Royal Proclamation of 1763, but due to the population imbalance, this was unrealistic.
So the British gave French speakers some leeway. With the Quebec Act in 1774, they allowed the mostly French-speaking Quebecois to keep their religion, to keep some of their legal customs, and to be involved in their government (perpetuating the power structures from the French colonial days). And the British did not try to impose the English language either. In return, the French speakers were loyal to the British crown.
Although Canada is an independent democracy now, with freedom of religion and (in principle) equal political participation for all, cultural factors are still strong. Quebec has an independentist movement, and has held two referendums on independence, in 1980 and 1995. Independence lost both times, but that's not because the Quebecois have been assimilated into the now English-speaking majority. A majority of Quebecois remain loyal to Canada because Canada allows them to keep their culture, and the French language is a very important element of that.
Canada is Canada because it puts French and English on an equal footing for official purposes, regardless of the population ratio.
