the IMT-affiliated Trotskyist movement in Canada previously existed in the form of Fightback, a network of campus organizations (I'm still on their mailing list because of a guy I met at university who tried to sell me newspapers). I think this leaves the current layout at 3 communist parties; the new Revolutionary Communist Party (RCP), the IMWCP-affiliated Communist Party of Canada (CPC), and the formerly Hoxhaist and internationally un-affiliated Communist Party of Canada (Marxist-Leninist) (CPC-ML).
the history of the CPC-ML is pretty fascinating, it was founded in large part by Hardial Bains, who was a member of the Communist Party of India's youth wing during his childhood in Punjab but quit over the CPI's acceptance of Khrushchev's criticism of Stalin. he remained a hardcore anti-revisionist, and when he traveled to Canada to study bacteriology he ended up as, essentially, the leader of the Maoist New Left in Canada.