Here are a couple of links to website that have volunteer opportunities. The range of opportunities is wide and most sites are searchable using your criteria of choice including short and long terms and kind of work.
Featured Volunteer Job
Volunteer Vancouver. This is the most established volunteer agency in Vancouver with many large organizations posting volunteer jobs.
GoVolunteer Mostly Vancouver, Lower Mainland, Edmonton and Virtual
Pacific Immigrant Society The are not currently recruiting.
VGH Research Institute -volunteer to be a in a clinical trial as a subject or control group. There is a wide range of studies for all ages and for those who are healthy or have health conditions.
The City of Vancouver- A variety of volunteer jobs are available including some on boards.
One to one tutoring This site requites volunteers for schools in the Vancouver to assist students with practice reading. A clinical record check is needed but it is free. A three hour training session is provided and you can pick the schools you prefer as well as am or pm shifts.
Local, Across BC and Canada
The Red Cross The Red Cross is my favourite volunteer experience. I worked there as a volunteer in their call center during the Tsunami in 2004. There were well organized, smart and fun.
CUSO Note that you have to make a $ 3000 contribution to partially self fund or fund raise.