Here are some excellent resources for finding big trees:
Port Renfrew Ancient Forest hiking guide: Be sure to check out the local forest conservation group, Ancient Forest Alliance, hiking guide to the extraordinary trees near Port Renfrew, BC.
http://bigtrees.forestry.ubc.ca/ BC Big tree registry lists the largest, tallest and widest known trees for most native BC tree species, with some info on there location. Follow instructions on the website to submit your own record-sized tree.
http://vancouverislandbigtrees.blogspot.ca/ An interesting resource for finding big trees as well as information and perspective on a variety of subjects pertaining to old-growth forests.
clubtread.com A meeting place for the Vancouver hiking community. This is a great place to meet other hikers or to submit questions on a forum a local hiking expert can likely answer.
Trails Venture BC has recently published an up to date map of the North Shore hiking trails. I have not seen it yet, but the authors explain that they have mapped significant trees across the area.
Outdoor Vancouver is a free online hiking guide. They have added excellent directions to visit the infamous large remaining cedar tree in Lynn Valley.
Back Road Mapbooks ($25-30) are essential for travelling along BC’s backroads and they conveniently label many notable trees. Find this at MEC or most highway gas stations.
The only official local big tree hiking guides were published by Randy Stoltmann and the Western Canada Wilderness Committee in the late 1980s and 1990. These are out of print but can sometimes be found, if your lucky, at used book stores or online book distributors such as Amazon.