Even if your rabbit is small and friendly, it’s not a good idea to introduce it to your guinea pig as a long term companion. Rabbits can be very docile animals and are a great companion for humans, but there are two reasons why they’re not ideal hutch-mates for guinea pigs. Firstly, rabbits are often gentle but are also liable to kick during what they consider to be play time - it’s in these circumstances in which a guinea pig can be seriously injured. Secondly, they’re not a good substitute for another guinea pig. If you have a guinea pig living on its own, then it needs a guinea pig companion to keep it company as rabbits and guinea pigs don’t have the same communications systems. How would you feel never being able to talk to someone? By far the kindest thing to do for your pet is to get it a friend of the same species.
Guinea pigs should be kept away from rabbits
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.