It involves buying an interlisted stock in CAD, having the broker journal it over to a US exchange, and then selling the stock for US$. Only fees paid are on the purchase and sale of the security, which Questrade charges $4.95....but in your case, the fees might come out closer to $20 (since you'll be buying a large amount of shares)
The technique is called Norbert's Gambit. I've used DLR.TO for this in the past, since that is a very liquid ETF that trades on both the TSX and NYSE
However, if you do this for very large sums of money, there are caveats
1) You'll be subject to price fluctuations in the US dollar if you use DLR.TO...this can change your proceeds and result in taxable gains if you do it in a taxable account.
2) It takes time to execute (minimum 4 days for trade settlement, plus around 2 days for Questrade to do the journal)
3) The price difference between DLR.TO and DLR may not be exactly the prevailing exchange rate.
4) There are specialty houses for converting currency that use way better rates....this is worth looking into as well
Also, I've never actually withdrawn the USD. Questrade may apply additional fees for this. Usually when I do this technique, it's to invest in US listed securities. However, I can't see any fees being even remotely close to the expected $7,500 you'd paid to a bank to convert CAD/USD.