Insurance companies do not typically sell short term insurance for one day. In fact, usually the shortest term is 6 months for an insurance policy. Instead of getting US insurance to pick up the car and drive it home it will likely be easier for you to see if your current Canadian insurance provider will add the car to your policy.
The Insurance Corporation of British Columbia (ICBC) provides universal auto insurance to BC motorists. The ICBC is also responsible for driver licensing, vehicle registration and licensing so you might speak to them concerning how to get insurance on the vehicle you are picking up from Washington state and then how to register it.
If you are importing a vehicle into BC from the United States, it is suggested that you contact the Registrar of imported vehicles (www.riv.ca) or call them at 1-888-848-8240.
If you do not currently have insurance on a vehicle and need to get a Canadian car insurance policy for your newly acquired vehicle, you can start here by getting a quote.