Driving sister's car to the US: what do I need at the border

I am borrowing my sister's car for a month and driving from Vancouver to California. What sort of paperwork will I need at the border to have no hassles? I am not the owner, but have permission to take it. Thanks in advance!

Letter from your sister with contact details on it. I'd check with the insurance company too before you do it.

Hi Steven, any issue if I am borrowing the car to move to CA from Calgary/AB?

I have an L1-B visa and am planning to drive the folks car across to move me and a few things, they will fly in a week and drive it back. I can get a letter of permission from them.

They are checking with the insurance company too.

Thank you, Lise

No different whose car it is. letter of permission, check with insurance.