This is a never ending question on here. Currently, the GBP = 2CAN$, fluctuating either a few cents higher or lower, based on the day's trading and whether you are buying or selling them. Your best rate will always be obtained by taking the CAN$ from the ATM here as you will get the day's exchange rate. However, the service charge from your UK bank may be large and end up defeating the value of this method. If you arrive here with GBP, there is only one place to change them really, and that is to find a Thomas Cook currency exchange shop. The rate there will be higher as the per centage charged for using the service is built into the rate you get. Despite people saying that a bank did the exchange for them, some banks will not because of the 'money laundering' legislation which requires a report of large sums of foreign currency be exchanged to be sent to the government. Just about all banks here require you to have a bank account before they will do business with you. Don't bring travellers cheques either. So, all in all, maybe not the best exchange rate, but the one with the least hassle would be to buy the CAN$ in the UK. But, having been back and forth to the UK many times, the difference is paltry and not worth wasting time on it. In other word, you have spent a lot og quids on the trip, and now you are worrying about a few pence difference in exchange. Doesn't make a lot of sense in my view. Just think of it this way. Everything is half price here.