Victoria is something I hadn't thought of - thanks. Trying to balance interests of a 21 year old with what we want to see is interesting....

Thinking of flying in and out of Seattle since it's cheaper, and doing the train both ways - I hear that's quite a scenic ride. Any words of wisdom on the train? Was hoping we wouldn't need a car in Vancouver so glad to hear that's the way to go.
I've never been to Vancouver without a car, so I don't know about how practical that would be.
Didn't take the train, but I am a rail enthusiast. You're going to need the same travel documents that you would need by car. I'm thinking you're not likely to need one of the trusted traveler cards, an enhanced driver license/ID isn't going to be available to you, and you'll probably want a passport and/or passport card. If you fly in you're going to need a standard passport.
The train would be the Amtrak Cascades, and they have a few cross-border trips daily. It's recommended that you check in 45 minutes early if you have luggage, and of course there may be a line. It's a nice station, but there really isn't that much there yet since it's been remodeled.
I would second the recommendation for the Capilano Suspension Bridge, although I'm not sure what it's like taking a tour bus. There is some sort of public bus service, but I would think you'd be riding the bus a lot. If you're worried about traffic, I found that BC drivers are ridiculously polite.
Another interesting thing there is some of the best Asian cuisine in North America. Chinatown is somewhat dated, but the new Chinatown is much of Richmond, BC. I've been to parts of China, and it has a similar feel these days. More than half the population self-identifies as Chinese.