Christianity is the most common religion in Canada, with 53.3% of the total population or 19.3 million people being Christian in 2021. The preamble to the Canadian Charter of Rights and Freedoms refers to God. The French colonization beginning in the 17th century established a Roman Catholic francophone population in New France, especially Acadia and Lower Canada (now Nova Scotia, New Brunswick and Quebec). British colonization brought waves of Anglicans and other Protestants to Upper Canada, now Ontario. The Russian Empire spread Orthodox Christianity in a small extent to the tribes in the far north and western coasts, particularly hyperborean nomads like the Inuit. Orthodoxy would arrive in mainland Canada with immigrants from the eastern and southern Austro-Hungarian Empire and western Russian Empire starting in the 1890s; then refugees from the Soviet Union, Eastern Bloc, Greece and elsewhere during the last half of the 20th century.

The majority of Canadian Christians attend church services infrequently. Cross-national surveys of religiosity rates such as the Pew Global Attitudes Project indicate that, on average, Canadian Christians are less observant than those of the United States but are still more overtly religious than their counterparts in Western Europe. In 2002, 30% of Canadians reported to Pew researchers that religion was "very important" to them. A 2005 Gallup poll showed that 28% of Canadians consider religion to be "very important" (55% of Americans and 19% of Britons say the same). Regional differences within Canada exist, however, with British Columbia and Quebec reporting especially low metrics of traditional religious observance, as well as a significant urban-rural divide, while Alberta and rural Ontario saw high rates of religious attendance. The rates for weekly church attendance are contested, with estimates running as low as 11% as per the latest Ipsos-Reid poll and as high as 25% as per Christianity Today magazine. This American magazine reported that three polls conducted by Focus on the Family, Time Canada and the Vanier Institute of the Family showed church attendance increasing for the first time in a generation, with weekly attendance at 25 per cent. This number is similar to the statistics reported by premier Canadian sociologist of religion, Prof. Reginald Bibby of the University of Lethbridge, who has been studying Canadian religious patterns since 1975. Although lower than in the US, which has reported weekly church attendance at about 40% since the Second World War, weekly church attendance rates are higher than those in Northern Europe.

As well as the large churches — Roman Catholic, United, and Anglican, which together count more than half of the Canadian population as nominal adherents — Canada also has many smaller Christian groups, including Orthodox Christianity. The Egyptian population in Ontario and Quebec (Greater Toronto in particular) has seen a large influx of the Coptic Orthodox population in just a few decades. The relatively large Ukrainian population of Manitoba and Saskatchewan has produced many followers of the Ukrainian Catholic and Ukrainian Orthodox Churches, while southern Manitoba has been settled largely by Mennonites. The concentration of these smaller groups often varies greatly across the country. Baptists are especially numerous in the Maritimes. The Maritimes, prairie provinces, and southwestern Ontario have significant numbers of Lutherans. Southwest Ontario has seen large numbers of German and Russian immigrants, including many Mennonites and Hutterites, as well as a significant contingent of Dutch Reformed. Alberta has seen considerable immigration from the American plains, creating a significant Mormon minority in that province. The Church of Jesus Christ of Latter-day Saints claimed to have 178,102 members (74,377 of whom in Alberta) at the end of 2007. And according to the Jehovah's Witnesses year report there are 111,963 active members (members who actively preach) in Canada.

Canada as a nation is becoming increasingly religiously diverse, especially in large urban centres such as Toronto, Vancouver, and Montreal, where minority groups and new immigrants who make up the growth in most religious groups congregate. Two significant trends become clear when the current religious landscape is examined closely. One is the loss of 'secularized' Canadians as active and regular participants in the churches and denominations they grew up in, which were overwhelmingly Christian, while these churches remain a part of Canadians' cultural identity. The other is the increasing presence of ethnically diverse immigration within the religious makeup of the country.

As Mainline Protestants and Roman Catholics have experienced drastic losses over the past 30 years, others have been expanding rapidly: overall by 144% in 'Eastern' religions during the 1981-1991 decade. Considering Canada's increasing reliance on immigration to bolster a low birth rate, the situation is only likely to continue to diversify. This increased influx of ethnic immigrants not only affects the types of religions represented in the Canadian context but also the increasingly multicultural and multilingual makeup of individual Christian denominations. From Chinese Anglican or Korean United Church communities, to the Lutheran focus on providing much needed services to immigrants new to the Canadian context and English language, immigration is making changes.

For some Protestant denominations, adapting to a new secular context has meant adjusting to their non-institutional roles in society by increasingly focusing on social justice. However the pull between conservative religious members and the more radical among the church members is complicated by the numbers of immigrant communities who may desire a church that fulfils a more 'institutionally complete' role as a buffer in this new country over the current tension filled debates over same-sex marriage, ordination of women and homosexuals, or the role of women in the church. This of course will depend on the background of the immigrant population, as in the Hong Kong context where ordination of Florence Li Tim Oi happened long before women's ordination was ever raised on the Canadian Anglican church level.

As well a multicultural focus on the churches part may include non-Christian elements (such as the inclusion of a Buddhist priest in one incident) which are unwelcome to the transplanted religious community. Serving the needs and desires of different aspects of the Canadian and newly Canadian populations makes a difficult balancing act for the various mainline churches which are starved for money and active parishioners in a time when 16% of Canadians identify as non-religious and up to two-thirds of those who do identify with a denomination use the church only for its life-cycle rituals governing birth, marriage, and death.

Evangelical portions of the Protestant groups proclaim their growth as well but as Roger O'Tool notes they make up 7% of the Canadian population and seem to gain most of their growth from a higher birthrate. What is significant is the higher participation of their members in contrast to Mainline Protestants and Roman Catholics. This high commitment would seem to translate into the kind of political power evangelicals in the United States enjoy but despite Canada's historically Christian background as Lori Beaman notes neatly "...[forming] the backdrop for social process" explicit religiosity appears to have not effectively moved the government towards legal discrimination against gay marriage. Much as many Roman Catholics in Quebec ignore the Church's stance on birth control, abortion, or premarital sex, the churches do not dictate much of the daily lives of regular Canadians.