I'm on an old farm in Pitt Meadows, about a half hours drive from you. Below our many Cedar groves we have a ground cover-Cornus Canadensis, a bleeding heart species and trilliums along with Ivy and periwinkle and various ferns. Most every-thing dies back in the winter. It's a joy to watch the ground come alive and bloom in the spring. This farm is about 150 years old. I have looked around and no other actual shrubs seem to survive under the Cedar trees here.
I am also having to find plants to go beneath a cedar...I have been taught to look at nature for inspiration, what grows under cedar trees in the wild? We have salal, sword ferns, deer ferns, lady ferns, red huckleberry, foam flower, mahonia nervosa...hope that helps