Weather in the Pacific Northwest is very changeable. May is often great weather, but not all tourist things may yet be open for the season. Summer is a great time to visit, and the middle two weeks of September is often the best weather of the year. (Not too hot, crowds are down, tourist shops offering end-of-season discounts.) Prepare for sun or rain, and dress in layers. You’ll be fine.
Puget Sound cuts the area in half, and a lot of things to see are on opposite sides of the water. There are few bridges, driving all the way around takes a long time, and you’ll usually need to catch a ferry, which in itself is pretty cool. A kind of mini-cruise, for not a whole lot of money.
Combining a whale watching trip with a timeshare stay requires knowing where and when for both. WM in Deer Harbor is a nice, quiet area on a beautiful island, but it’s more of a destination than a base camp for visiting a larger area. They do whale watching tours from that island, but also from Anacortes, and I think even from Seattle or Vancouver. WM The Camlin in Seattle gives you major urban options - it’s central to the metro area, but it’s also about 90 minutes plus traffic to Anacortes, where you catch the 1.5 hour ferry trip to Orcas Island, where Deer Harbor sits. The WM resorts in Blaine and Birch Bay (which are actually next door to each other) are freeway-close to Seattle (about 100 miles away, no ferry required.) But it’s another destination location, and is limited on tours. WM Discovery Bay is on “the Peninsula,” and is a good base camp for exploring the Olympic Nat’l Park area, but it’s otherwise pretty quiet in that area. (Port Townsend is the closest town to it, nice to see, but can be done in a few hours.)
I’d say plan a mix of your time. Stay in Seattle for as long as you want to check out the metro area, then go to Deer Harbor for a few days so you can go whale watching and enjoy the San Juan Islands. Then maybe try Vancouver or even Victoria, and whale watching from there, if it doesn’t work from the U.S. side. They have Orca pods in that area, too.
No solid answers, I’m afraid. There is a lot of options up here.
Dave