Weather in/around Seattle at that time of year is difficult to predict. Historically, that's part of the rainy season (the rains typically have ended on July 5th, like clockwork) but with climate change, in recent years things have been drying out earlier - it's a roll of the dice.
As a Seattle resident, I'd caution you to calibrate your expectations for whale watching around here, especially at that time of the year. There are generally 2 kinds of whales one can see here: California Grays (which are predictable, reliable and plentiful, but inconveniently located out off the coast, hours of driving from Seattle; they're also not here in large numbers when you will be - they drive by in the fall and spring, so you would be a couple months late for optimal viewing).
As noted above, the orca population is dwindling and everyone is freaking out and floating proposals for stern measures to save them, including banning all whale watch boats for years - my reading of the local tea leaves suggests this will happen but will probably take a couple years as everyone goes through the motions and the political theater known as "the Seattle Process".
So I would caution against high expectations for whale watching around here, especially on a trip where you have limited time. If you've previously had an awesome close encounter from a Zodiac then I think what you'll find here may disappoint.
About those mountains....the Canadian Rockies (even just the Washington Cascades) are serious mountains, not at all like the hills you've seen back east. Yes, you get real winter there in the upper midwest, but when you spread that ice across all those very, very steep mountains, it's a very different experience from driving I-75 through Saginaw, even when it's iced over. Be careful if you tackle the passes through the Canadian Rockies, even in late spring.
Honestly, I think you are trying to bite off too much for this trip. It's big out here. Need to pick and choose. You've got no more than 12 days, including travel - so after subtracting the flight days you've got 10 days - not enough for all the things on your list.
Pick either the coastal stuff (Seattle, Vancouver plus nearby places), or the Canadian Rockies including the long (but very pretty) drive to/from Vancouver.