Answer: Because you say you "need... arguments," I'm assuming your task in writing this "History essay about a quote" is to agree or disagree (or perhaps both) with the assertion contained in the quotation, in this case, Trudeau's claim that "Canada will be a strong country" if the conditions expressed in the two when clauses become true (and you'll probably have to define what Trudeau means—or what you think he means).
Explanation: I'm not sure what Trudeau meant by this quote, but I believe he was referring to one of the most important issues in Canadian history: the linguistic, ethnic, and cultural divide between Canada's French-speaking population, which is concentrated in the province of Québec, and the English-speaking majority, which predominates in the rest of the country. Trudeau was notable for his efforts to bridge this divide and foster Canadian unity, not only through the passage of the Official Languages Act/Loi sur les langues officielles, which established equal status for French and English at the federal level, but also through his leadership during the October Crisis of 1970, which resulted from terrorist acts by Québec separatists.