I'm going to be traveling from the U.S. to Canada by myself (age 16) without any adults. I'm planning on taking a bus, and I was wondering what all I'll need. I've looked up online plenty, and the requirements are different per-site which isn't helpful. I'm currently not emancipated, and I do not have a passport.
Canada will admit US citizens with any proof of citizenship, such as a US birth certificate, along with photo ID. The two can be the same document, if course, if you are using, for example, a passport. Source: http://www.cbsa.gc.ca/travel-voyage/td-dv-eng.html#_s2a
The US, on the other hand, requires more secure documentation. These requirements are codified as the Western Hemisphere Travel Initiative (WHTI). The WHTI has less stringent requirements for those under 16, which doesn't help you.
You should therefore most likely get a US passport or passport card. The latter makes sense mostly if you are planning not to travel to other countries in the next ten years, or if you plan to travel by land or sea, relatively frequently, to Canada, Mexico, or the Caribbean.
If you live in one of the states that offer them, you also have the option of getting an enhanced driver's license or state DMV non-driver identification card.
Finally, you should also ask the bus company about their requirements, since these could be more restrictive.