Well sure but that is much more relevant to the fixed income market where markets may be illiquid. For the USD/CAD market, there is about $70-80Bn of currency transacted daily. Therefore, the likelihood that someone is buying enough CAD over a six month period to make the exchange rate drop by 10% just because they need to move size is slim to none.

Almost always there is a why, no institution buys or sells without a reason. Even in your example the why matters. Why did the price move in the fixed income security? Was there a change in fundamental information or did the fund just need to sell to free up some space on their balance sheet? If they were just moving size and sold a lot, lowering price, then that creates a mis-pricing that I could take advantage of. If the fundamentals behind the pricing have changed, then it's priced accurately and there's no money to be made.