In some situations, you will have a contract with the Real Estate agent, who then contracts with the owner. The Real Estate agent is a managing agent and performs all the administrative duties and tasks. In other cases, the owner pays a set fee to the agency for renting out the property. The landlord then deal with you directly after the contract has been signed.
Every Real Estate company has their own office; some agents have offices in several Canadian cities. Depending on what you are looking for, it can be a good idea to contact them to increase your available options.
There are accommodation and relocation services who can help you locate suitable properties and even arrange viewings. There is normally a charge associated with this type of service, so make sure they look reputable before paying over the cash. Online, you can find information about many rental properties available on the websites of estate agents and specialised sites for property. If you are looking to share an apartment, you can also find other people online. A good place to start is in the classifieds at Just Landed!