Hey Guys.
I do this all the time. I take out a wad of cash in Canadian $. I take my wad of cash to the CIBC. I ask to buy a bank draft in U.S. $. At most Canadian banks, you can get it drawn on a U.S. account. They do this as a matter of course at the CIBC with their U.S. sub, an NYC bank.
Then you mail your draft. Done.
Since it's drawn on a U.S. account the U.S. casher doesn't pay any penalty for drawing a foreign cheque. The charges on the U.S. side should be zero. The charges on the Canadian side are a small flat fee for cutting the cheque (if it's your bank it might be free) and whatever premium they take on exchange, which is usually about the best rate you'll get on the exchange.
In my experience, you can't beat this. Especially for large sums. For getting a tube here, a cable there, credit cards are way better.
Cheers.