I looked into Interactive Brokers in more detail and you are correct that their fees are extremely low. They do not seem to charge a hidden "spread" fee, which is they usual method that forex traders hide their fees.

Based on some googling, there are secondary fees to consider such as minimum monthly fees and wire transfer fees, which might make it more or less attractive than alternatives depending on conversion amounts and regularity of transactions.

You mentioned that you use Interactive Brokers. Are you a Canadian citizen living in Canada that transfers money into and out of an Interactive Brokers account, exchanging USD and CAD?