You may want to post on the forum below for more infor for your area.
How cold will your winters be? If there's the possibility that the water will freeze solid, what do you intend to do with the fish?
IMO, if you're going to have fish, it's not fair to not have plants that they can enjoy nibling on. Goldfish don't tend to destroy plants like Koi, so whatever you put in there shouldn't be affected by the fish.

Will this container be getting partial, full or no sun? That will determine what plants you can use. If you want something that blooms, consider water cannas, iris, and waterlilies.
There's lots to choose from and you'll have the container filled in no time!

Here is a link that might be useful: Ponding, water gardens

I have a bunch of internet pond friends in BC. You can grow tons of stuff with little effort. Parrot's feather, pickeral, cattails, horsetail, various rushes and reeds, hardy waterlilies (stick with small ones like Helvola or Perry's Baby Red) There really are many choices.

Depending on what part of BC you're in (it's a BIG place!) you could grow the same stuff I'm growing here in WA state. I've been pulling stuff up from natural ponds and streams where legal. I've got a lot of native wetland stuff that way. Yellow monkey flower, creeping veronica I pulled out of a lawn actually but it's a wetland plant, coltsfoot, piggyback plant, water parsley. Duckweed from a friend's pond, necessary to cover water surface to reduce algae. And the goldfish will eat it. I've also got Japanese iris, they're perfectly hardy here in USDA zone 7/8. And some native sedges etc I don't know the names of, and a small hardy water lily from the nursery. Just ask at the nursery what they've got that's hardy.

goldfish will eat pretty much anything and they need a lot of space as they're very dirty fish. A 50 gallon tank shouldn't have more than a couple or three goldfish for optimal health of plants and fish. They'll keep the mosquitoes down, but they'll also eat any frog eggs or damselflies or water beetles. I keep the fish out of the pond and use floating Bt tabs for the mosquitoes.

In the winter, even our mild winters, my 25 gallon tub will freeze over but never so far solid. I cut the plants back after frost and sink them to the bottom of the tub for the winter so they'll be protected from the cold by the water. That just means that I take any supports out from under the pots so they're all sitting on the bottom. Then when it warms up in spring I pull them out and put the bricks and stones back under them. So long as the water doesn't freeze solid the goldfish will be fine but don't feed them in cold weather. They need to go into like suspended animation over the winter and feeding them will make them sick.

Consider how to set it up so it's not a buffet table for raccoons. Fish as the entree. Raccoons are quite strong and inquisitive and can move rocks and rip out plants.

Good point eric! I've had raccoons destroy the plants in a 12' x 15' pond and they also managed to get a few of the goldfish, which is what they were after.
After seeing the destruction to the pond I could envision the raccoons doing the backstoke between meals!

I have my main pond surrounded by an electric fence because of the masked tornados that some call raccoons.

My pond is 3 ft. deep with straight sides and no ledges. That works great. Raccoons will not swim or dive. They see with their hands and must touch and handle everything. I once had a washtub on the deck with goldfish and rocks. Can you say "buffet table"?

Beg to differ eric........;)
Raccoons are excellent swimers.........they just don't dive. They had to be able to swim to reach the lily pots in the middle of my pond, 12' across.
For more info google 'raccoons swim'.

I never said they can't. Is it common for them to swim? I didn't think so.