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 

Be a puppy parent for a Guide dog. BC and & Alberta Guide Dogs  Puppy training   

Vancouver

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

UBC Volunteer patients, Faculty of Medicine

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

Charity Village

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.

List of volunteer centers across BC

International

CUSO   Note that you have to make a $ 3000 contribution to partially self fund or fund raise.