A Canadian Prime Minister can, at best, hope to have some influence at the margin as a kind of voice or reason.
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When the leaders of several middle-sized powers  - Canada, Australia, The Netherlands, The Scandinavians, Poland, Spain, Brazil, Mexico, South Korea, Italy, etc., etc., all take a similar view, their combined weight can sometimes affect the outcome of larger decisions.
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And sometimes they are ignored, all the same.  That's life for a middle power.
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Canada excelled in this role under Borden, St. Laurent, Pearson, Mulroney, and Chretien.  Chretien was brilliant.
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Mackenzie King, Bennett, Diefenbaker, and Harper all stank at diplomacy.  No clue.
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Better for Canada to have a positive image as a country that tries to be thoughtful and helpful, than a miserable, negative, misanthropic image, as under Harper, that just turns everybody off, and reduces our in influence from very little (at best) to absolutely zero, or negative, (the norm under Harper).