@Mayana , after a quick look at this thread, I would like to clarify ----
There are two different characteristic that I think is being confused -----
1. monies invested for personal purposes ( i.e. personal wealth / asset / property . In this case
(a) if you chose to invest domestically , then all gains are generally taxable be it as ordinary income ( interest, dividend etc. ) or capital income ( short term or long term ) but losses are generally only recognized partially ( applicable generally only to capital assets. Sometimes you can also use casualty loss under certain circumstances..
(b) If you choose to invest in foreign assets ( ordinary or capital ) you assumed to recognize the currency risks and therefore whereas gains are taxed, losses may or may not be recognizable, assuming also that your operating currency is US$ ------ this implies that losses of the earnings are recognized but the loss of principle is generally NOT.
In you particular case with Canadian T-bills, loss of principle due currency fluctuation is not recognizable ( you are expected to have known or should have known the risk ) because this your basis/ investment but the gain loss can generally be offset against other ordinary or capital gain loss. I don't know if I am being clear -----
If you need more help on this I would be only too glad to help ,
pk
