Ontario Universities’ Info is a great place to start researching university programs. You might find it helpful to review the programs that interest you, develop a possible list and then narrow your program options. Keep in mind that certain programs have prerequisite courses that you must successfully complete (or be in the process of completing) in order to apply.
When you’re researching, keep track of information you might need later on in the application process. For example, find the OUAC program code, a 2- or 3-letter code, for each university program that interests you and keep them close by for easy reference when you apply.