The short answer to your question is that it is not the only factor. The exchange rate, as I mentioned before the committee the last time, is a relative price, in the sense that it's the price of the Canadian dollar relative to the U.S. dollar, or the Canadian dollar relative to the euro. So there are a number of factors that impact that exchange rate. In the Canadian context, commodity prices have historically proven to be an important explanatory factor for movements in the Canadian dollar over time, but there are other factors that influence the dollar as well.
On February 26th, 2008. See this statement in context.