I used to fish this area quite a bit years ago. Lots of halibut at the channel head but you have to fish it during slower tide movements. Rupert has the biggest tide changes on the BC coast, 20ft+ tide changes happen every month. Generally if your on a big tide shift day (17ft+ change), don't bother fishing if the tide is moving fast in the channel. Fish only on plus or minus (1/2hr) on either slack tide. Definitely wait for this 'shift', it can be deadly but its only for a short period. On the low tide change days (14ft-), you can sometimes fish throughout the tide change and catch fish.
If you a bigger boat and you want halis, fish the outside.......plenty of hali out there and BIG.