If you have an Electronic Travel Voucher issued in USD, but you want to redeem it for flights within Canada, you can have the Voucher converted to CAD first. Otherwise, you may end up paying US taxes to the US government without even touching on a US airport.

Here's my story: Due to an oversold flight departing from a US airport, I have an "Electronic Travel Voucher" (which is actually a paper slip you can not use online, but only over the phone), issued in USD. I wanted to use it for a oneway flight wholly within in British Columbia, Canada (YCG->YYJ).

But the taxes would have ballooned from CAD 32.xx to USD 46.xx. The AC phone agent told me that two US taxes would be added - although I am not touching any US airport. :-(

The solution: They can convert the voucher's balance from USD to CAD (and at a reasonable exchange rate at that). Then the ticket can be issued in CAD, and no US taxes apply (unless they apply due to the itinerary, obviously).