I can't answer your first question, unfortunately, but I will throw my two cents in on the second one.
We have done both the dolphin swim and the day resort packages. The dolphin swim is an amazing, albeit short, experience (about half an hour in the water, plus the orientation time beforehand).....but the opportunity to be that close to a dolphin is something that memories are made of. For a first visit, if the budget allows, I would strongly recommend booking the dolphin swim. You'll be able to see the other guests interacting with the dolphins as you walk along the beach, and you will crave the opportunity to take part in that experience too.
That said....
If the dolphin swim is going to completely blow the vacation budget (and as a fellow Canuck, I totally feel your exchange rate pain), the day resort admission will also give you an amazing day at a much lesser cost. The only thing you will miss out on is the dolphin experience.....everything else is exactly the same. You will still see the otters, the marmosets, go snorkeling in the Grand Reef, etc.
So for *us*, it was worth it to do the dolphin swim at least once (we have actually done it on two of our three visits, as we took a DC newbie on trip #3 and that warranted giving her the dolphin experience, too). When we go in October (assuming OUR budget will allow!), we will just do the day resort package and save the difference.
Have you considered doing just the day resort package at DC, and going to SeaWorld and adding on a tour there instead? Dolphins, sea lions, etc? That would give your kids an animal interaction experience at a MUCH cheaper cost....and your admission to SW is included with your DC package.