The United Church of Canada is the largest Protestant denomination in Canada. We minister to over 2 million people in about 3,000 congregations. The history of the United Church is closely entwined with the history of Canada itself.
The United Church was inaugurated on June 10, 1925 in Toronto, Ontario, when the Methodist Church, Canada, the Congregational Union of Canada, and 70 per cent of the Presbyterian Church of Canada entered into a union. Also joining was the small General Council of Union Churches, centred largely in Western Canada. It was the first union of churches in the world to cross historical denominational lines and received international acclaim. Each of the founding churches had a long history in Canada prior to 1925. The movement for church union began with the desire to coordinate ministry in the vast Canadian northwest and for collaboration in overseas missions. Congregations in Indigenous communities from each of the original denominations were an important factor in the effort toward church union.
The United Church continues to be a "uniting" church, and has been enriched by several additional unions since 1925. In 1930, the Synod of The Wesleyan Methodist Church of Bermuda became part of The United Church of Canada’s Maritime Conference. The Evangelical United Brethren Church became part of The United Church of Canada in 1968. In addition, various individual congregations from other Christian communions have became part of the United Church over the years.
The Wikipedia entry on the United Church also offers an overview of the church’s history and background.