Well, no, they wouldn't go into specifics as it's a song book which which seems to be aimed at, say, school history lessons and social singers. In the Penguin Book of Canadian Folk Songs there is the additional reference to an essay by Fowke: " 'The Red River Valley Re-Examined', Western Folklore, 23, 163) Presumably the proof is in there. If no one comes up with anything along those lines, try the ethnomusicology/SEM list and the Canadian Folk Music Society (or whatever it's currently called).

I'm not sure I see how "A Lady in Love" published in 1889 predates the Riel rebellion ...

sian