A few bus companies, including e.g. Bus Asia, offer service between Kuching, Malaysia, and Pontianak, Indonesia, both on the island of Borneo (Kalimantan).
Plugging those cities into Google Maps reveals a few different routes that might do the job, crossing the Malaysian/Indonesian border at Entikong, Jagoi Babang, or Aruk; it is possible that other routes may be possible as well.
However, visitors to Indonesia from many countries may apply for a Visa on Arrival or pick-up a pre-reserved Electronic Visa on Arrival only at certain border posts. Entikong and Aruk are on the lists, but Jagoi Babang is not and so should be avoided by visitors from those countries who do not wish to obtain a regular tourist visa in advance (which costs IDR 1,500,000 instead of IDR 500,000 and is also more annoying to obtain).
If I am considering undergoing a trip such as this one or elsewhere on Borneo, how can I learn what border crossing the bus is likely to use and thus if I will be able to use the VOA or e-VOA service?