If you were using paypal then it would allow the user to pay in any currency and in a way increase the target audience and wouldn't possibly put a buyer off.

If you are worried about currency fluctuations, would it be possible to have a US bank account which profit would enter which would then be used to pay for anything US based therefore decreasing risk when converting $CAD to $USD? If so, then you would only transfer money to $CAD when the currency rate falls into a certain range for example 0.95-1.xx