Seattle and surrounding area in 8 days
 

My husband and I are planning 8 days in Seattle and would like to include Olympic NP, San Juan Islands Anacortes North Cascades NP, Leavenworth, Mt. Ranier, Mt. St. Helens. I'm having a hard time narrowing it down. We will be there in early June. Help!

If you look at a map of Olympic NP you will see that there are no "through" roads. You go to the end of the road and then have to backtrack. At Mt. Rainier you may still have some snow alongside the road at high elevation in early June.
Try to spend at least one night somewhere east of Portland on the Oregon side of the Columbia River. Multnomah Falls is well worth stopping at and taking a hike.

June is late Spring in Seattle. July and August are our summer months.

Taking into account what has been said about snow at Mt. Rainier NP, here is one possible routing to do most of what you want to do: Seattle, Mt. Rainier, Olympic NP (via Olympia and Lake Quinault), Anacortes (via ferry to Whidbey Island from Port Townsend), San Juan Island (or Orcas Island), North Cascade NP (via Highway 20), Winthrop, Lake Chelan, Leavenworth (via Highway 2), Seattle.

I left out Mt. Saint Helens because the visitor center for viewing the mountain is a slow 55-mile drive from I-5 and a slow 55-mile drive back to I-5.

HTtY

PS Highway 101 circles Olympic NP. To visit sites within the park (Hoh Rain Forest, Hurricane Ridge, etc.) one must drive from 101 to the site and then back to 101. Lake Quinault, Lake Crescent, and Sol Duc Hot Springs are some of the sites on or very near 101. Hurricane Ridge is a 17-mile drive from Port Angeles.

Thank you. That sounds like a good addition to the trip.

Do you think there is time to visit Victoria BC in there, or am I really overextending?

You can visit Victoria as a day trip from Port Angeles: https://cohoferry.com

Or, If you take your car to Victoria, you can take a ferry from Sidney, BC, to Friday Harbor on San Juan Island and then from San Juan Island to Anacortes and on to North Cascade NP.

If you want to take the Sidney or Coupeville ferry, book well in advance.

HTtY

PS Many would say you are overextending, but there are instances I want to see as much as I can in a short time. Therefore: Seattle (1), Mt Rainier to Lake Quinault (2), Port Angeles (3), Victoria (4), Friday Harbor (5), Winthrop (6), Seattle via Chelan and Leavenworth (7), Seattle (8).

In case Mt. Rainier is shrouded in clouds, you may want to spend more time in Seattle at the beginning of your trip and drive to Olympic NP via the scenic stretch of 101 that skirts the west side of Hood Canal.

HTTP has provided a good plan but I would probably skip the San Juan islands with the time you have or just do Seattle (2 days), ONP (3 days) and San Juans (3 days) and skip the Cascades. To put the timing in perspective, we've taken separate trips where we spent several days to a week in each of the mentioned stops and felt it was too little time. For an 8 day trip, without San Juans, I would plan as follows (and even then I couldn't quite make 8 days as I have you returning to Seattle on Day 9):
Day 1 - Seattle - explore city, Pike Place market, terrific dinner and music or pub scene
Day 2 - pick up donuts at Top Pot doughnuts and drive to Mount Rainier, go for a hike, overnight in Olympia
Day 3 & 4 - drive to Quinault - 2 nights at Lake Quinault Lodge, with a day trip to Hoh rain forest (the lodge can arrange), play in lake, relax on the lawn (or drive further and do overnights at Kalaloch Lodge at beaches or Crescent Lake). Lake will be cold, ocean will be colder.
Day 5 - stop at Ruby beach for morning walk (unless you stayed further north), Port Townsend stop for ice-cream at Elevated Ice-Cream Co., overnight in Oak Harbor on Whidbey Island (I love Langley but it is on other end of the island).
Day 6 - drive to Winthrop, on the way stop at the Washington Pass overlook. Lunch and walk around Winthrop (I think we watched the rubber duck races from the back patio of Old Schoolhouse Brewery and enjoyed a terrific lunch & brew, we also went to a glass studio at one end of town). Consider Freestone Inn in Mazama for lodging and dinner.
Day 7 and 8 - Lake Chelan (highly recommend a day trip by boat to Stehekin with a Rainbow Falls hike). Also we've enjoyed blueberry picking, wine tasting, and for sure buy some pie. I ate pie everyday when we visited Lake Chelan. You can swim in the lake, rent jet skis, play miniature golf or play tennis. Or, more wine tasting.
Day 9 - drive to Seattle with stop in Leavenworth on the way. Fly home (late flight).

The above trip looks a little like an infinity symbol with a loop through ONP and a loop through the North Cascades. I think both loops could be done individually as 5 day trips so you should probably determine the pace at which you want to be traveling, how much time you want on the road (gorgeous scenery, fun stops on the road, short hikes to an overlook) versus activities (kayaking, boating, hiking, exploring, relaxing).

love the Northwest, whatever you decide plan for rain but it could be sunny and gorgeous

I meant to type HTtY, not HTTP, anyway completely agree about the weather as it will make a difference as to whether the drive to the Mountain is worth it.

also if you go to the islands by ferry be mindful of the ferry schedules and plan to arrive well in advance to catch the ferry, especially with summer travel.

You have been so helpful...thank you.

Our top picks from the Olympic Park circle were Kalaloch Lodge area, including Ruby beach and the haystack rocks around there along with Hurricane Ridge. If you see the Ridge, drive up there and enjoy the view. We lucked out on a summer evening in Port Angeles. We went up for an evening view with every intention of going back up in the morning. In the AM, the ridge was fogged in and you could not even tell there was a ridge there. Completely cloudy. So, if you see an opening to get up that 17 miles...go for it. The view was fantastic.