why bank account in Canada must contain only Canadian Dollars??

[wired]

why  bank account in Canada must contain only Canadian Dollars??  I have US $'s sent to me and have a US $ bank account in canada.  Want to keep them as US $'s.

[blaast]

same here!

I opened a USD account at my canadian BANK, in order to be able to withdraw money even when the exchange rate isn't favorable. But then, Paypal doesn't allow it? I understand they can charge their own exagerated conversion fees on cross currency withdrawals but preventing withdrawals within the same currency is a questionable method of creating a monopoly on money conversion.