For this 4%, you can do nothing since most banks are the same in Canada.你的钱会一分布少地按银行的买入价换成加元。我实在不懂你为什么认为有可能可以避免这个“官方”差价。Consult a financial broker if you'd like to. Anyway, if there is no difference, what's the purpose to do foreign currency exchange?