The Charles Reiner Collection consists of correspondence, newspaper reviews and clippings, performance programmes, personal documents including legal material, photographs, writings, published and unpublished music by Reiner and other composers, audio and visual recordings of Reiner and other performers, books, and awards. Of particular interest is correspondence from Rudolf Serkin, Alfred Cortot, and Kurt Waldheim; legal documents from both before and after Reiner’s immigration to Canada; and the extensive collection of programmes and newspaper clippings that document Reiner’s extensive performance career.

Three volumes of choral sheet music from the Choir’s library were donated to McGill University by the Estate of D. Torrance Fraser, a former choir member, in 1926. The pieces in these three volumes are second copies of those pieces found in Series 1. In 1927, another volume of sheet music from the Choir’s library was donated to McGill University by the Estate of D. Torrance Fraser. This fourth volume (DTF2) contains many pieces not found in the other volumes.

Gould's papers fall into two series. Family correspondence covers the years 1856 to 1860, when Joseph and his brother Charles were travelling in Europe, and consists of letters home from both young men, and their parents' replies. Manuscript music comprises two volumes of church anthems, with some organ music; some are original compositions by Gould and Samuel Warren. Related to this is Gould's brief manuscript account of the origin of the Mendelssohn Choir. Some family photographs are also included.

The Montreal Mendelssohn Choir Collection comprises several volumes of sheet music from the Choir’s library. The choral folios were compiled and bound into eight volumes at the time of their donation to McGill University in 1895. The estate of D. Torrance Fraser, a former Choir member, donated another four volumes of choral music in 1926 and 1927. Three volumes contain second copies of the pieces from the Choir’s library donated thirty years prior; the fourth volume donated in 1927 contains a number of pieces performed by the Choir but not found in the seven extant volumes from the Choir’s library.

The Montreal Mendelssohn Choir donated eight volumes of choral sheet music from the Choir’s library in 1895, a year after the Choir’s dissolution. There are only seven extant volumes in the collection because volume 6 has been missing since at least the 1980s.

The Roger Doucet Collection consists of over 1000 pieces of sheet music (including scores), 45 manuscripts, and one scrapbook containing photographs and newspaper clippings related to his career as the singer of “O Canada” during professional sports games.