Why not just use a forex broker instead? Better rates, lower spreads, and higher liquidity. I would personally recommend Interactive Brokers.
For example, according to the calculator, converting $100k saves about $350 versus a 0.3% conversion fee. Even converting $10k is cheaper than 0.3%. What are Interactive Brokers fees?
Another reason is that you don't have to transfer your money out of your accounts to a third party. Everything happens within your brokerage accounts.
I'm not 100% sure on the fees but they are not even close to 0.3% for forex. It's pretty much around $2 for most trades (their example covers: USD 50,000 daily volume for EUR = USD 2.00). Here are the details of the fees: https://www.interactivebrokers.com/en/index.php?f=commission...
I think the reason IB charges are so low is because they deal with very large customers (banks, trading houses, etc.).
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?
My email address is in my profile if you want to get in touch with more questions :)
After some further research, it does seem like Interactive Brokers is a good option for the OP. For posterity, here are two blog posts by a Canadian describing how he uses Interactive Brokers: http://blog.plsoucy.com/2012/11/best-way-to-convert-usd-to-c... and http://blog.plsoucy.com/2013/03/converting-usd-cad-interacti...