First off, I am just getting started, it's been over twenty years since my last aquarium. Thanks to everyone for all the great advice.
Now to the point, I have worked for FedEx and now I work for a passenger airline. Every plane has a heated cargo compartment so shipping pets by air is not a problem. FedEx will not accept pets for shipment (unless your a zoo). I would use which ever airline is in your area (probably Air Canada) and see what kind of cargo service they have. We offer flight specific shipments, mostly for dog and cat breeders and a lot of fish from Florida, but also some personal pet shipments. You pick the flight you want you fish to depart on and you will know exactly when they will arrive. If you had the time you could even be on the same plane as they were (except you would have a seat up top and they would be down below). You will pay a premium for this service but it is better than the post office since you will know their schedule just as you would if they were a passenger.
This way you can set up a new tank, have someone ship them (or fly back and do it yourself), meet them at the airport when they arrive, transfer them to your new tank, and have happy fish.
Here is a link to AC Air:
http://www.aircanada.com/cargo/en/products/document/acexpedair_can.pdf
Hope this helps.