There are a few different ways to determine camera reliability, but for the most part, it comes down to two things: build quality and customer service.
When it comes to build quality, Canon and Nikon are typically at the top of the list. These companies have been making cameras for decades, and they know how to build them to last. Their flagship models are especially well-built, with weather-sealed bodies that can take a beating. If you're looking for a camera that will last you a long time, either of these brands is a good bet.
Customer service is another important factor in determining camera reliability. If something goes wrong with your camera, you'll want to be able to get it fixed quickly and without hassle. Here again, Canon and Nikon excel. Both companies have extensive service networks that can get your camera repaired relatively quickly. They also offer extended warranties on their products, which can give you some peace of mind in case something does go wrong.
So overall, if you're looking for a reliable camera brand, Canon or Nikon is probably your best bet. They both make high-quality products that should last you many years, and they both offer excellent customer service in case something does go wrong.