Seals are pretty common along the Halifax coastline and sometimes
this happens. I've also seen a couple whales and porpoises in the harbour, and there are mackerel, cod, and various invertebrates in the harbour. Seabirds include various gulls, shearwaters, terns, osprey, and cormorants, black ducks and mallards will go in the ocean occasionally but seem to prefer lakes, as do loons. Every once in a while we'll get algae/plankton that makes the harbour glow red, or leaves streaks of green light when objects travel through it.
In the more urban parts of the municipality squirrels (small red one) and raccoons are pretty common, deer and foxes somewhat less so. Rats are common along the waterfront. Bears, coyotes, and porcupines occasionally wander into areas around the outskirts but aren't at all common. Beavers and muskrats are fairly common in the lakes. Halifax is a bit of an anomaly within Canada since the urban area peters off into forest rather than farmland and I guess the local ecology reflects that (a few other cities are like this but most seem to be directly adjacent to farmland). It also partly explains the frequent conservation battles alluded to in the post above - greenfield development here usually involves cutting down a lot of trees. I don't have the stats to back this up but I would guess that the native tree species are among the most biodiverse in Canada. Wild blueberries, raspberries, blackberries, cranberries, pincherries, and occasionally saskatoon berries (possibly feral?) are found scattered throughout the area. Liberty cap mushrooms also grow wild in a lot of the city parks. Apple and cherry trees are fairly common as decorative plants in people's yards but not to the same degree as in Vancouver. The city has also started experimenting with palm trees, I'm not sure if they last the winter or if the city just replants them each year.
Stuff like green roofs, living walls, bioswales, small planted areas adjacent to sidewalks, and extra landscaping on public property is becoming more common and the city has actively been planting trees all over the place since completing the Urban Forest Master Plan a few years ago. Emphasis is on local species, and there's also a trend of planting stuff that's potentially edible (but primarily decorative). Community gardens and such are becoming more common as well and there are organizations dedicated to stuff like urban beekeeping. The harbour seems a lot "healthier" since the sewage treatment system got upgraded but I don't have any stats to back this up.