Go to http://www.ets.org/gre/general/register/index.html for general pre-registration instructions, like considering when to take it, the advantages of the paper and computer versions, fees, and number of times it is beneficial to take the test. The computer-based and paper-based tests can only be taken once a month and not more than five times within a consecutive 12-month period.
Decide whether you want to take it on the computer or on paper. For the computer-based exam, click, the corresponding tab on the left. If you wish to register online, click "Online Registration" under the Web section. Fill in the Country/Location box in the next step with Canada. Select your Canadian city. Wait to receive a response on whether there are test centers in that city or not. If there aren't, you will have to travel to take it. If there are, click to register. Choose Ontario as your state. Click on "Schedule an Exam" in the following step. Call 1-443-751-4820 or 1-800-473-2255 to register by telephone or use the mailing instructions on this Web site: http://www.ets.org/gre/general/register/cbt/index.html.
Choose the "Paper-based Test" option if you wish to take it via those means (http://www.ets.org/gre/general/register/index.html). For web registration, click "Online Registration" and create a new user profile if you are not a returning user. Call 609-771-7670 to obtain the GRE Registration Bulletin and Supplement required to register for the paper-based test. Go back to the Web site mentioned previously in this paragraph and choose "Test Centers and Dates" to the left. Download the Test Center List PDF and check under Ontario provinces for the one you'd like to take it in. Call the number provided to register in your Ontario home town.