More doable but I wonder if you should drive to Victoria (save a lot on seaplane fares unless you want the experience) and then go down to Seattle. Not sure what you want to do there but I think 2 full days is more than enough.

From there, drive to Penticton (or Osoyoos) via the North Cascades Highway (US-20?) if it's open and then up US-97/BC-97 over night. Can drive to Banff the next day.

This way, you get to go through less unpredictable border process/quieter crossings which won't take as much time.

On the return from Banff, stop in Kelowna as you wish and then straight to YVR the next day for your return flight. It's a 4 hr drive but I'd give yourself 6 just in case, or have one extra day in Vancouver.