Canada and australia are (mainly) english-speaking countries with populations that are not too different in size (canada's is 60 percent larger). but canadian trade is twice as large, relative to gdp, as australia's.
why should this be the case?

Canada and Australia being located on both other ends, thus have a wide  travel duration. Canada is richer than usa.

Explanation:

Canada is currently the second-largest goods trading partner of the U.S, China, and the U.K in terms of export and imports with a total trade of $617.2 billion. The goods export trades totaled to $298.7 billion, while goods imported totaled to $318.5 billion. Canada is n the northernmost part of the world experience high trade volumes and this is mostly due to the nearby countries as Australian country is located far south it does not have a large trading partner so the amount of the trade participation is less. Time taken for the goods to get delivered and deposited is also more as compared to the American and Canadian standards.

Themes; subfields is the answer