"Hyak" did a great job summarizing a list of some of the species at the aquarium, and here are the aquatic mammals that I saw yesterday:
Pacific White Sided Dolphin - 2
Beluga Whale - 2
Harbour Porpoise -2
Sea Otter - 3 (including one that is blind)
Harbour Seal - 2
Stellar Sea Lion - 2
Northern Fur Seal (off-exhibit)
Other than the Northern Fur Seals I've seen all of the other species on each of my 4 visits this year so you should have no problem at all. In regards to birds there are 7 African Penguins in an outdoor exhibit and the rest are in the small Tropical Rainforest walk-through area. Yesterday I saw the 3-foot long, free-roaming Basilisk lizard and that was a highlight as that critter is often very elusive in the rainforest zone.
In regards to reptiles and amphibians there is an excellent section called "Frogs Forever?" that has 22 exhibits with various species of frog, toad and newt. Throughout the aquarium there are various other herp exhibits featuring anacondas, a boa constrictor, a green sea turtle, poison dart frogs, Yacare caimans, etc.
Unfortunately for you it is not a great time to be visiting the aquarium. Clownfish Cove, the kiddie section with a few tanks, has been completely taken apart and that area is now non-existent and due to be relocated near the 4-D Theatre. That accounts for 2 construction zones inside the aquarium, plus the entire outside area is awash with construction as the new entrance plaza, indoor restaurant, gift shop, etc, makes its debut in 5 weeks. The aquarium can become crammed with visitors and the expansion (even without any new animals) will be brilliant as it will spread out the overwhelming crowds and school groups that are seemingly around every corner. The Tropical Rainforest has 2 more construction zones as at least 8 exhibits have been closed for months (Jamaican fruit bats, turtles, electric eel, piranhas, pufferfish, etc) and a large replica of an Amazonian tree trunk with a dozen invertebrate species (various tarantulas, centipedes and scorpions) is also closed. There are several temporary jellyfish displays that are blocking permanent exhibits and the entire aquarium really is a bit of a mish-mash at the moment. After June 13th it will be immeasurably better and so you'll have to keep that in mind during your visit. However, even with all of the closures there is still a lot to see and the aquarium is bigger and better than anything to be found in either Australia or New Zealand but it still is nowhere near as impressive as Monterey Bay Aquarium in California.

I would rank Vancouver Aquarium as the #7 best aquarium I've ever seen and I'll have toured more than 50 by this August.