Rabbits and guinea pigs are not a perfect match. Even if your rabbit is the smallest and friendliest bunny you've ever met, there can be problems.
Rabbits can be quite violent - an unneutered male, especially. They may also try to mount the guinea pig, which can cause the GP distress, and even injury. Even a very docile one - and there are many of those - will be liable to kick as part of their play. They may mean no harm, but a bunny kick can injure a guinea pig.
Hop it! Guinea pigs and rabbits just don't mix
A rabbit is no substitute for another guinea pig. If you have a GP living alone, it needs a companion - and that companion simply has to be another guinea pig. Rabbits and guinea pigs have different body language and communications systems, so they simply don't understand each other. It would be like a human condemned to live on a desert island with a gorilla who only speaks Old High Norse! So, always get your guinea pig a friend who speaks the same language - i.e. a member of the same species.
If you want your guinea pigs and rabbits to meet, then a solution would be to create a mesh partition between their areas. This way, they can see and smell each other through this ‘wall’, without your rabbits being in any danger of accidentally harming your guinea pigs.