Bear is right about the ferries. WA ferries are just in Puget Sound.

Here is the WA ferry website:
http://www.wsdot.wa.gov/ferries/

I suggest you start in Vancouver, spend a bit of time there.
Take the ferry to Victoria. Enjoy a day or two there.
Take the clipper fast catamaran service (see link above) to Seattle.
Take train to Portland.

Vancouver / Victoria is great in August. Sun doesn't set until around 9:30pm. Summers are glorious.

The ferries are busy in summer. If you have a (rental) car, be certain to reserve a spot in advance. Or you could take a taxi to the Tsawwassen terminal and walk on the ferry. Then take a taxi from the Swartz Bay terminal to Victoria. You don't need a car in Victoria. It's small and great for walking. A bus will take you to Buchart Gardens.

I don't think there is a direct train Portland to Vancouver. I think you have to change to a different rail or bus line in Seattle. That's why starting in Vancouver would be best.

Enjoy your trip and happy anniversay!

Fly to Vancouver, spend a couple days there, then take the amazing Rocky Mountaineer train to Whistler for the day and return on seaplane to Vancouver early evening. My parents did it and they said it was amazing.

There's at least one through Cascades service RT daily Portland-Vancouver, but who knows if it will survive into 2016. Most services do require a change in Seattle which is a good reason to get off and see something of the Emerald City.

And if you book via Amtrak, mind that you don't select a bus service by accident -- several "Amtrak" journeys are actually operated by "Thruway Bus" which will be pretty grim trips up or down Interstate 5.