If you just need some cash, you can withdraw U.S. currency at a bank machine using a Canadian debit card, but there are fees involved. Travelers cheques are also a good alternative, as they take only 1 business day to clear and are relatively safe to transport.
Once you have bank accounts set up, you can also look into an online currency exchange service like XE or Custom House. These companies are a foreign exchange providers for businesses and speculators, but they are happy to work with individuals and students. They offer good rates (they guarantee better than any bank) and they they don't charge any fees beyond the exchange spread. It takes a few weeks to set up an account (which is free, but involves some paperwork and security checks), and doing a transfer usually takes about a week. They can transfer the money electronically between your U.S. and Canadian bank accounts. If you're going to be sending large amounts of money reasonably often (for tuition, etc.) then this is a great way to save some money.
Wire transfers are the quickest way to transfer money, but may incur large fees for both sender and receiver. The Canadian bank may also require your authorization to make the transfer and transferring large amounts of money (over $10,000) could cause a security check that will slow down the process significantly. To set up wire transfers from your Canadian bank without going to the branch in person each time, sign a verbal/fax authorization before leaving: this gives you the power to initiate transfers from your account by either calling or faxing your contact or branch manager.
A simple, but slow, way to transfer money is to write cheque to yourself from a Canadian account denominated in US dollars -- ask at a branch for details.