The United Church was inaugurated on June 10, 1925 in Toronto, Ontario, when the Methodist Church, Canada, the Congregational Union of Canada, and 70 percent of The Presbyterian Church in 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.
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. Click the link below to view the service bulletin from The United Church of Canada's inaugural service on June 10, 1925, held in the Mutual Street Arena, Toronto.
https://archive.org/details/unitedchurchofca00unse_0
Source: united-church.ca/community-and-faith/welcome-united-church-canada/history-united-church-canada