Lucky things! We've just come back from a trip to the rockies, the wine region, vancouver & the island. Absolutely wonderful. Jealous, we didnt make it to the islands west coast.
Take binoculars. Big country, lots to see at a distance.
Banff lovely, Jasper isnt. Recommend glacier, hot springs, cable car trips for the view. See crowds, stop, they are usually looking at animals. Wine region (Kelowna is centre. Summerhill Winery great, friendly, excellent wine). Canadian Molson lager goes down a treat on a hot day, as does Canadian dry white wine. Their real beer is good too.
Vancouver itself - Stanley park a must. Hang around the picnic areas and you may see raccoons.
Vancouver Island - I'd emigrate tomorrow if winters were a tad sunnier. We went whale watching on a rib raider (rubber boat with engines!) with only 6 seats, rather than the bigger touristy boats. If you are into adrenalin - wow! We encouraged our 'driver' to really hit the waves and it was GREAT. We were kinda sore the next day admittedly.
Longhall Flights - make sure you exercise your legs, even while sitting. Drink lots of water. TAke sleeping tabs (prescription or something like Nytol) with you so you can get a decent kip. If you want to listen to inflight system, your own headphones may be comfier. Loose clothes and comfy shoes essential! If you can get bulkhead seats you will have more legroom, but possibly less width as they have to slot the tables into the sides of the seats. Keep small amount of freshen up toiletries in hand luggage. Warning - Vancouver Airport shops etc ALL currently close at 8-9pm, biggest first.
If flying overnight, try to get a seat on the correct side of the aircraft. That moment when the sun just rises/finally dips is unforgettable. A window seat will give an amazing view of the plains if you fly over during daylight.
ENJOY!