Stephen Gordon, writing at Worthwhile Canadian Initiative, has a very revealing graph (reproduced here):
The upper, dashed blue line represents Canada's trade surplus with the US from 2002 until the present; the lower, solid blue line represents Canada's trade surplus with the rest of the world. From 2002 until about two years ago, Canada's trade surpluses remained roughly constant and positive. Put bluntly, we were sending more of our goods and services to foreigners than they were sending to us.
Two years ago, the surpluses started to decline a bit, but they are still surpluses! Canada is still sending more goods and services to foreigners than they are sending to us.
And this high demand for Canadian stuff just keeps putting upward pressure on the Canuck buck, as shown by the red line in the graph. There's a tendency to think that because the Loonie is appreciating, our trade surpluses will decline, but that phenomenon (analogous to a movement along a demand curve) is more than offset by the continued growth in demand (shift of the demand curve) caused by rising oil and commodities prices.
Digression: Stephen also has some poignant insights about The Bank of Canada in his recent postings -- well worth reading.