Hi Flutterbye,
I think you had a two legged visitor, a heron. They can clean out a pond pretty quick. A net is a good idea, and 3' bamboo stakes around the pond will help.
Since you are starting over, yes the pond needs a very good clean, all mulm from the bottom needs to be removed. If there is nice fluffy algae on the pond walls.. leave it there as it's helpful. If there are any plants in the pond now would be an ideal time to repot them into fresh soil(regular topsoil with a bit of clay mix).
Question for you, is this a rock bottomed pond(ADI aquascape type) or just a bare liner bottom?
Once you've got the cleanup finished try and find a place to rent a water meter and use this while filling the pond so you will have an aqurate gallonage - this is important if for any reason you might have to treat the pond with medicines/chemicals. Let it sit for a couple days(with the pump running) to bring the water temperture up. Before adding fish add a dechlor like amquel or prime to knock off any residule chlorine/chloramine.
Fish..., Where in Canada are you? You can add goldfish again if you like them. Wakin are quite hardy and very lively pretty goldfish. Shubunkins are fun colourful goldfish with flowing fins. Depending on the gallons/size of your pond you might be able to add Koi or Golden Orfe, these fish tend to get rather large and need lots of space(water).
BTW, pond filters should be cleaned on a weekly basis... a month is too long.