The Canadian dollar weakened during foreign exchange trading yesterday (October 20th) after the country's central bank warned that the loonie is becoming too powerful.So named because of the bird on the dollar's reverse face, the loonie has climbed strongly against its US counterpart in recent weeks, bootstrapped by stronger demand for crude and a greater appetite for risk.Commenting on the upward momentum - which has led some analysts to predict that the two North American dollars will hit parity - the Bank of Canada warned that its strength could "more than fully offset" recent signs of economic growth witnessed in the country.Export revenues from the sale of oil and gas to the US would be put under particular strain by exchange parity between the two currencies.Speaking to Bloomberg, David Watt, senior currency strategist in Toronto at RBC Capital Markets, a unit of Canada's biggest bank, described the central bank's comments as "pretty much a frontal assault on the currency".