My husband & I are spending a week in Seattle in October & would like to visit Victoria, BC also. Timewise, is it reasonable to go to Victoria, explore, spend the night & return to Seattle the next day or would two days be better? Also, what would be the best way to get to Victoria?

Take the ferry across. It is easy. Victoria is a wonderful city.

Yes, from Seattle on the Victoria Clipper is a great 1 night trip!

You could also combine Victoria with a vist to Olympic National Park, taking the ferry from Port Angeles.

It depends on if you want to bring your car. If not, the Victoria Clipper is a great way to go. If you do want your car, then you will need to drive further north, to Anacortes or Tsawwassen (BC). From there, you can take a car ferry to a ferry terminal near Victoria. As noted above, you could then take the Black Ball ferry to Port Angeles, visit Olympic National Park, then return to Seattle (requires one more short ferry hop). The latter choice would be quite ambitious for only two days.

Since it's October I think it's worth the warning that you may need sea-legs on the Clipper. I had a horrible trip in steep seas and don't recommend it for the seasick set like me. I like ALF's suggestion of the Black Ball. Head to Port Angeles on day 1 and take the afternoon ferry to Victoria. You can walk the entire inner harbor. There are buses if you want to go to Buchart Garden (but that would take most of your day). Return to PA on the afternoon ferry the next day. See Black Ball at www.cohoferry.com. See also www.tourismvictoria.com. We did this trip last weekend, so ask any other questions of me and others. Enjoy.

Thanks for all the advice. We hadn't planned on taking a car. Can we see enough of Victoria on foot & via public transportation?

you can see much of Victoria on foot -
I suggest Willy's for breakfast
The Blethering Place or White Heather for the traditional high tea ( this is where the locals go) Might want to take a cab there -
If you decide to take the car the ferry from Tsawwassan is the prettiest ride.
I would suggest spending a night in Victoria