What's the cheapest way to buy $US from Canada?

I have an account with Bank of Montreal (in Canada) and another one with Wells Fargo (in the U.S).





I was wondering what is the cheapest way to make a deposit in my Wells Fargo account:





- Using Paypal to withdraw $CDN from BMO and transfer it in $US and then deposit at Wells Fargo.





OR





- Withdraw $US directly at BMO and pay their currency rate. After I can make a deposit at Wells Fargo next time I go in the States.





OR





-Any other idea??|||I use a service called Hyperwallet which charges 75 cents, but they hit you hard on the exchange rate. Your PayPal idea isn't bad, but I don't think you can hook up both US and Canadian accounts to a single PayPal account, and if you transfer between two PayPal accounts, you have another 2% hit for doing the transfer. The cheapest way for sure is to withdraw $USD cash and then deposit it in person in the US, but that is also by far the most inconvenient.