Mackenzie King was a diplomatic disaster area - in some ways not unlike Harper, ironically.
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FDR led us out of the Depression.
FDR and Churchill led us through WWII.
Both FDR and Churchill had sanguine, and not flattering, assessments of WLMK.

Mackenzie King thought that Adolf Hitler was "a man we could do business with".  His idea was to have the Canadian Army sit out the war at camps in southern England, preferably without ever fighting.
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As a consequence, most of the Canadian Army landing in Normandy had no battle experience, was relatively poorly prepared, and suffered larger than necessary losses as it made mistakes in Normandy.
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That is why 1st Canadian Army was subsequently relegated to secondary tasks along the Atlantic coast, and why it was heavily criticised for delays in opening Antwerp to shipping.   By contrast, in WWI, the Canadian Corps (and the ANZACs) had been "the shock troops of the British Empire".
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Canada's principal Allies strongly distrusted Mackenzie King.