There is a website and service called Hit The Road which is an automobile delivery service. The company matches people with car delivery needs with people with transportation needs. The owner of the car pays a fee to have their car delivered to a specified destination. The driver of the car receives a small fee (basically gas money) to pick up and deliver the car. The company is based out of Canada and most of the opportunities are within Canada and between Canada and the United States. There are some rules and regulations, but hey... sounds like a cool way to see North America overland for travelers with flexible schedules.
Check out the Hit The Road website of FAQs.