Near Seattle
Whole day: Rainier is both a cool place and a very nice drive.
Whole day: North Cascades Ntl Park
Whole day: Go to Leavenworth for a day, take the south route (US90) on the way and the north (2) on the way back. Stop over at the Snoqualmie Falls Hydroelectric Museum, then go have some tacos at Caadxi Oaxaca a few blocks away and keep driving east and stop over at the Franklin Falls and do the mile hike, my kids loved it. Once done with that keep driving to Leavenworth and have dinner there, great bratwurst/icecream and nice little town to visit. The drive is great. The way back is amazing on route 2, it will probably get dark by then.
Two days: probably best to find a place in Port Angeles (I found an airbnb for one night): Olympic National Park is a great places to visit. You have Ruby Beach, Hoh Rain Forrest, Hurricane Ridge
Portland:
Grab some subs from Sammich Restaurant and head over to the Multnomah Falls, lots of hikes. Keep in mind in order to get into that area by car you need to get a permit, they have time slots, so get an early one. They are limited. Spend time there, then head over to Mt Hood. I am not sure Mt Hood is worth it in itself, but the drive is great. We did a bunch of hikes over at the mountain though so we liked it.
Vancouver
Grouse Mountain. We had the most fun here, awesome place full of activities.
Rent a bike and do Stanley park.
Lynn Canyon Park. Do the hike, its free and in my mind better than Capilano. You have the hanging bridge, the 30 foot pool, etc. Awesome hike
I could go on and on, but I need my wife to refresh some of my memory :D
Note 1: Keep in mind crossing into Canada will take the best part of an hour unless you have NEXUS. They will ask for passport and where you staying/what you are doing. Also keep in mind that the speed limits in the whole PNW are quite low, and people respect them, so drives take time.
Note 2: If you do a couple of parks, its worth it to get the annual national park pass. You can buy it at some of the parks entrances and it will last 13 months. If you have a kid in 4th grade, its free. You can also buy it at the REI Coop store (222 Yale Ave N), as a matter of fact, there is a Park Ranger office there and they can give you a bunch of maps/info and the store is cool.