Unfortunately its all in person knowledge from living in the area.

Coast Salish Agriculture: permanent exhibit at UBC Botanical Garden. Specifically how they cultivated groves of Garry Oak trees.

Searching Garry Oak or Garry Oak Tree turns up a fair bit of resources to read there.

In general, a bit to read about a non PNW native agriculture is a short excerpt in The World Without Us by Alan Weisman. He talks about what we consider the "natural state" of the island of Manhattan. To paraphrase: If you consider it plains or meadow, that's not the natural state. That state was one created and managed by native people in the area when European explorers and settlers arrived.

As for their use of the western red cedar. Again, in person. For in person visits and information I would recommend:
• Grouse Mountain maintains a small collection, as well as some respectable Alpine-ish hiking in the summer.
• Sea To Sky Gondola in Squamish, BC: tourist attraction run by the local native band.
• The best would of course be the UBC Museum of Anthropology. Edit: which works with the native groups to display/restore/preserve artifacts. Its not just pilfered stuff.