You have to have a degree from one of those programs AND THEN you have to pass a test. You can do urban planning without it (If I'm not mistaken you don't go for your test until you've been working in the field for at least 4 years), but you can't sign off on any plans until you are certified and most positions require that you're eligible for OPPI/CIP membership.
Keep in mind that in Toronto alone there are probably over 200 students working towards their bachelors/masters in urban planning. Finding volunteer/intern opportunities is extremely difficult for students (and it's a requirement as part of their planning degree) nevermind people who aren't in that stream already. That's not to say it would be impossible for you to call up some planning firm and ask to volunteer, but if they aren't doing it for people working towards planning degrees it seems unlikely that they would bring people in from outside that area unless you have something specific you can offer them.
If I were you and really wanted to pursue planning I'd look into Masters programs. It's your best chance.
EDIT: Actually, if you look here:
http://www.ontarioplanners.on.ca/content/BecomeAMember/becomefullmember.aspx you can become a planner without a recognized degree but first you need a member to sponsor you (so essentially you need a planning position). Here are the requirements: Recognized Planning degree- 2 years experience in planning (minimum);
Degree in a related field- 4 years experience in planning (minimum); Degree not related to planning - 6 years experience in planning (minimum)
So a bachelor's in geography can lead to a planning position but it's an uphill climb.