Usd/cad
Disclaimer: I work for a forex company.
There are many causes to currency valuations. The most important are:
1. supply of money (monetary inflation)
2. demand of money
3. speculation
Supply of money is quite literally how much the country's reserve bank creates. Theoretically, if they were to double the money supply it would eventually cause everything priced in that currency to cost twice as much and for it to be worth half as much against all other currencies (if the others keep their supplies stable).
If there is a demand for money that outstrips supply, obviously that will increase the value of it.
Speculation increases/decreases the demand for this money in a short timeframe.
If you see a graph of the USD/CAD over the last year, you'll see that there was a huge increase in the value of USD as people, freaking out over the economy, rushed to buy US treasuries, creating a demand for the dollar. Now that the worst seems to be over, people are moving their money out again. At the same time, due to quantitive easing and the large deficits of the US government, the fed is expanding the money supply by a large amount. Canada has done almost no QE and has a relatively small deficit. Also, commodity prices have increased, creating a demand for CAD.
Now I can't say what the USD/CAD is going to do in the future as it depends way to much on what both our governments do. If things keep going like they are, you'll eventually see a greatly devalued USD. Remember that the US federal reserve can just as easily stop creating money and even destroy it if things get out of hand.