The (theorized) Route

View Theorized Route in a larger map

Optimally I would like to end in Japan, at Honda Headquarters in Minato, Tokyo, Japan.

This means that the Americas need to be done first, if the rest of the Asia, Africa and Europe are to be done without extra oceanic voyages. Starting in Northern Canada or Alaska, and descending through North America, Central America and South America down to Tierra del Fuego. Once the southern tip has been reached, starting the only trans-oceanic voyage would begin to take us to New Zealand/Australia.

Sunbathing up through the Great Sandy Desert, would put us in line to take on as many of the island countries between Australia and South East Asia. Driving up through Thailand, across Cambodia and into Vietnam before swinging around to take on Laos and Southern China. The journey would continue on through Southern Asia (Bangladesh, India and on into the Middle East). 

Currently, it seems the most sensible to divert at that point and take on Africa. Down the eastern coast and up the western. This puts us in line to hop over Gibraltar and the (easy and luxurious at this point) European leg of the journey. After driving all over Europe and into Scandinavia, the final leg of the journey would involve European Russia, Kazakhstan, Mongolia and Northern China.

The final bit would involve a hop, skip and jump across to South Korea and onward to Japan.