from what i remember, a high CAD is usually because of a lot of foreign investment into australia. interest, dividends and profits are then paid to overseas investors which pushes up net income. but all this borrowing from overseas isnt really paid back, it just builds up and up which increases net foreign liabilities
so high CAD -> high net income -> high levels of interests on debt -> high and ever increasing net foreign liabilities
not sure if that is 100% accurate cause BoP is worst part of economics, but the answer is something like that