Finding sponsors is mostly about social skills.
Traveling to help some sort of aid project, raise awareness or some other excuses seems to help in finding sponsors.
The actual trip is of little importance, just make it sound like an achievement.
For example, I know a couple who cycled all the way from Amsterdam, to the North cape, and then down to Cape of good hope. They did not have any sponsors.
In contrast, I recently read about a couple, with several sponsors, who planned on cycling all the way from Amsterdam to Barcelona. They and their sponsors presented it as an unprecedented adventure. They had lots of sponsored equipment, bikes and media attention.
Sponsorship also will limit your freedom
Keep in mind that making a sponsored trip is not just about receiving funding: the sponsor generally expects you to do something in return. This can be as simple as promoting their product, but could extend all the way to being present at some predetermined place at a certain date and time, give interviews or anything they choose to put in the sponsor contract.