A recording of a musical score is treated completely differently to the score itself - so the music included in the film would have a ? or "phonograph" copyright, but the actual score would have the normal copyright © for documents and sheet music: note that the issuing of a recording (?) doesn't mean the corresponding musical score is considered to have been published (©).
If Stothart died in 1949 he would be PD in Canada by now, but was the score ever published, as opposed to recorded? Also, there would be the post-1923 US copyright to consider, which doesn't take the decease date of the author into calculating the copyright duration.