I think you have it backwards - kinda. The value of your debt remains the same. If you owe $100 at 5%, it is still $100 @ 5% regardless of of the currency fluctuations. Assuming that 1USD = 1CDN, if the Americans were to devalue their currency to 0.50, where 1USD would buy $0.50 Canadian, the Americans could in fact sell commodities like gold that are traded in USD and get more "paper" for that gold.
In this scenario, 2 things would happen if the US devalued their dollar:
- The value of the USD will decrease relative to Canadian dollars (among others).
- The (relative) value of gold would go up because it will take more (devalued) USD's to buy an ounce of gold and gold is traded in USD.
The Americans could sell-off their gold reserves (or a portion) and artificially get more money for that gold. The feds then pay for that 100 USD debt from the proceeds... In the end, because the US devalued their dollar, (where 1 USD = 0.50 CDN), they debt (settled in USD's) was 1/2 of the relative original amount.
There are more issues at hand than just this, but perhaps this gives you a picture of what's possible.