I read Keynes' biography written by Skidelsky.
In 1939/1940, Keynes used to go to the USA, representing the British Treasury, in order to negotiate the land lease. Skidelsky told that in this time, both far-right and far-left in the USA opposed the direct participation in the war. The far-right, because of obvious motives. The far-left, because they think that America had no gains in helping the imperialist powers of France and UK. The left viewed the British Empire as a villain.
A lot of people saw their subjugation of a bunch of countries, including Canada, as evidence for not wanting to ally with them.