You can't really go to a native reserve and just hang out there and gawk. Actually I didn't know there was one on Sea Island, but I'm pretty sure it wouldn't be open to tourists. Most native people in Vancouver are just urban dwellers like everyone else. You can certainly see some very interesting native artifacts at the Museum of Anthropology at UBC. There is also a center for native studies at UBC and they sometimes have performances and cultural events there. There is also a Native fellowship center on East Hastings near commercial were they sometimes have cultural events. You could call and find out what's happening there. Here is more info.
http://www.vafcs.org/