Your itinerary is doable, but not "a relaxed vacation".

This sounds like the kind of whirlwind itinerary I would do and my wife would rightly point out is far too aggressive if the goal is a relaxed vacation. Trying to fit in Vancouver, Whistler, Victoria, Seattle, Calgary and Banff in just 12 days is a lot. I would probably cut out two of Whistler, Seattle, Victoria or Banff/Calgary in order to make the trip more enjoyable.

You could easily spend a couple of days in Whistler/Vancouver Island exploring around and doing activities (e.g. hike/bike Whistler if into that kind of thing). Also nothing wrong with a down day or two around Vancouver walking the sea wall/Stanley Park/dt neighbourhoods.

My $0.02.