I'd try to clear customs in Calgary rather then Vancouver. There's direct flights Huston/ DFW to Calgary and direct flights to WH on Air North or WestJet.
IMO I'd bring a good spotting scope and phone scope setup. You'll never regret getting good video and pictures. I find it annoying trying to share a spotter especially when you're watching sheep. If you and your guide have a spotter you can both look and talk through what you are seeing in real...