I lived in BC for a year (lower mainland), and my fiance is from PEI, so I'm familiar with both places. (We live in New Brunswick now)
I agree that it depends on what kind of vacation you're looking for. Also, if you have kids and what their ages & personalities are.
BC - Vancouver is fun, and there's lots of nightlife. There are a fair amount of things to see, but I found things quite expensive. If you plan on seeing touristy things when you go, or even eating out a lot, I highly recommend you buy an Entertainment Book (
www.entertainment.com) before you go. It has 2-for-1 coupons for tons of tourist activities and restaurants. The transportation system in Vancouver is great, so it's pretty easy to get around. There's lots of shopping too. I don't know if there's a whole lot for kids to do though.. of course there's the science centre and the aquarium, and Stanley Park to run around in, but in my opinion, PEI is much better for kids, although there's lots for adults to do too. Whistler, BC is neat to visit, even in the summer, and there are lots of outdoorsey things to do in BC, if you're into that. I agree that Victoria is just beautiful, and I've heard that Harrison Hot Springs is nice for an adult trip. Perhaps someone else will have some suggestions of things to do in BC with kids. One suggestion though: don't bother visiting the Greater Vancouver Zoo. We were there 2 years ago, and it's not very nice. Lots of single animals in cages. ONE giraffe, ONE elephant, ONE hippo... so sad! If you're that close, do a 3 hour drive to Seattle and visit their zoo, or stop into the Calgary zoo on your way. THOSE are fantastic zoos!
PEI - I disagree with the previous poster that there isn't much to do in PEI except Green Gables. I've been to PEI at least a dozen times in the past 5 years, and I still haven't seen everything I want to! I like touristy things though. It's great for kids, or the young at heart. There are lots of campgrounds, B&Bs, and hotels, because the Island is such a tourist destination. Everything is so well taken care of too, it's such a pretty province. Cavendish has the bulk of the tourist attractions. Some of the attractions on the Island insclue a small amusement park (Sandspit), a park for kids (Rainbow Valley), and tons of other interesting/weird attractions (Ripley's believe it or not, Captain Barts, the bottle houses, woodleigh replicas, fairy tale village...). Golfing is HUGE in PEI and some of the best courses in the country are in PEI. Most of them won't cost you a fortune either. There are also some good mini-golf courses. The beaches in PEI are the nicest in Canada. White sand beaches. The ones in Cavendish are gorgeous, but busy in the summer. Ask the locals for less-crowded ones. Some romantic things to do: Visit the bottle houses (although kids will also like this - just don't touch!

), have dinner and spend a night at Dalvay-by-the-Sea, stroll the beaches, rent a cottage, see a show in Charlottetown, go on an evening cruise, or go to the drive-in in Brackley. We also like strolling the boardwalk in Charlottetown with a 'Cows' ice cream. Mmmm...