The records left by a participant in an event (or by a close observer) are obviously of great interest to the historian. There are two possibilities: Either the source has been published (in which case it will be in the catalogue , like a book) or it remains in manuscript form and has not been published. For this assignment, restrict your research to published sources.
Memoirs, diaries, etc. are rarely published in the time of the events they concern. (The most interesting ones probably couldn’t be published until well after the people they discuss have died.) Separately published memoirs, etc., are organized within in the catalogue under specific subject categories, known as "subject headings" that include the words “Diaries” or "Correspondence” (e.g., “Frye, Northrop -- Diaries”). Do a search of the person's name along with the words "diaries" or "correspondence" :
The Dictionary of Canadian Biography, which currently mainly covers people who died before 1930, is the most useful source for memoirs, diaries and letters by individuals. Look for these in the bibliographies at the end of articles.
Modern secondary scholarly works, both books and articles, are often your best sources for published personal documents like these. If you do use modern secondary sources to identify these sources, be sure that the sources you have identified are indeed published ones, not manuscript ones that may not be accessible to you.