Thank you all for your thoughts and suggestions. This gives me a lot to consider.
I like the Tokina 11-16, but the price is about $600-700. Ebay has lots but most are form Hong Kong... Not TOO far out of my budget, but I wonder if the 2.8 is really worth the higher price for my needs. But everyone says it's sharper too.
I love the idea of 8mm, but I think that's a little wider than I need for this application, but wider would be better than not wide enough.
Having never used anything wider than 18, I'm trying to find videos demonstrating the difference between 11mm and 10mm. I know it's small, but if the 10 is just that much wider it might only make sense to go with the canon. The cost is better too, but the f4 could be a little limiting.
I'll watch some online samples now. My only concern is that it looks like a lot of the tour videos are shot using gopros or similar, so it's tough to get a good idea of the size I need.
Thanks for you help so far, it gives me a lot to get started on!
-Stephen