I am now in CANADA.
and I understood that for the people in Canada , there is no difference between the American $ and Canadian $. 1 US$ = 1 Cad$ .
and in the bank it would be worse because the real difference is low and the tax will be add so if you give 100 US$, you will take less than 100CaD$ so it is logical to buy the Canadian $ in Iran, As the Canadian $ is cheaper than US $ in our country.