Sure, Lester Pearson could have done so, but it would likely have been written off as so much grandstanding, given that Canada was not the ancestral nation (for lack of a better term) of the Corsicans. The (misplaced?) ancestral pride expressed by de Gaulle for Francophone Canadians was backed by France's status as a (declining rapidly) major power: in those days, France still sort of counted for something, as opposed to its present status of near-total irrelevance.
de Gaulle however was the one that got France out of Algeria, and suffered several attempts on his life cause of it. Saying something like that would boost his support if anything. Canada would look a bit silly.It's several years too late to say anything about Algeria, though I could see Pearson calling the French hypocrites for having fought so long (and, ultimately, in futility) to stop the cries of "Vive l'Algérie libre!"
However, while I can't see Pearson going this far, I could see Trudeau offering moral support to the May 1968 protesters, or at least holding them up as proof the de Gaulle doesn't know what he's talking about.
In response to the De Gaulle "Vive le Quebec Libre" speech, could Canada have done something equally as damaging to interfere in internal French politics? Like openly supporting Corsican independence?
If Pearson does try to get back at de Gaulle, how would that be perceived in Quebec? Would such a counter-attack have boosted the nascient sovereignty movement?