Victoria?
 

We are going to Seattle and Vancouver for 3 days each. We have been thinking of a side trip to Victoria, but don't know if we have the time or what the best way to get there is. Should we go from Vancouver or from Seattle? Can we make it a day trip or is that too much?

with only 3 days each, i'd save victoria for another time. you can do it in a day but much more enjoyable if you can stay over a night or two.

I spent 5 days on Vancouver Island, and I loved it. I would save Victoria for a later date when you can take in more of the island along with the city itself. Good luck.

Just came back from essentially the same itinerary. We spent 3 days in Seattle and 4 days in Vancouver. We did a day tour trip to Victoria and Butchart Gardens. Just like previous comments,you would want to spend more time on the island,but we were glad we took the trip,it was one of the highlights. Taking the guided tour would take about 10-11 hours of your time. We spent about 2 to 3 hours at each place (garden and Victoria),the rest of time was on the bus and ferry. It is place you would want to stay overnight and maybe take a drive to Tofino.

Doesn't Victoria fit in perfectly for those without a car? Not a side trip but on the way using ferries. Seattle to Victoria, Victoria to Vancouver; it's a surprisingly direct path and probably much more enjoyable than running the roads.

I lived in Victoria once and we used to do day trips to Vancouver all the time so I dont see why the reverse isnt possible.
Plan to catch an early ferry (say 8 or 9 am) from Tsawwassen (its too far to go from Seattle for the day) and you are in Victoria 2 hours later. You can then spend 10 hours there, as the last ferry back is at 11 pm. Its a long day, but I think its worth it.

You may wish to consider that in order to take a day trip to Victoria, you will have to give up a day in either Seattle or Vancouver. I'd give up Vancouver.