Treasury Bills (T-Bills) are short-term debt instruments issued by the federal government and sometimes by a provincial government. They are issued in terms of 91, 182 and 364 days, and are sold in large denominations. Investment dealers and banks then repackage the T-Bills into smaller amounts, such as $5,000, $10,000 or $25,000, depending on the term, for individual investors.
You might find when you shop for a T-Bill that the return is called the effective interest rate. T-Bills don't actually pay interest. The return is really the difference between the price the Bill is sold at (which is always less than face value) and what it is worth at maturity. Banks and investment dealers will often translate this into a percentage return that is like an interest rate and allows you to comparison shop with other investments.
Short-term debt securities are also called money market instruments. Despite the name, money is not traded in the money market. It's called this because products like T-Bills or short-term paper are almost as flexible as cash.
Guaranteed Investment Certificates or GICs are really term deposit instruments, not bonds. They are usually issued by a financial corporation like a trust company or a bank, which actually borrows the money from you in the same way that it borrows from you when you put your money in a savings account. They use the funds to meet their own needs and pay out interest before paying you back in full on a set date. You usually keep a GIC until maturity, but some issuers will redeem their own certificates before maturity for a little less than their full value.