A project can recieve funds and issue its tokens from any number of blockchains it chooses from the set of eligible ones, currently Ethreum mainnet, Optimism, Arbitrum, and Base.
Under the hood, a juicebox project is deployed independently on each chain. They can have matching rulesets and payouts, or be totally different.
The juicebox projects on the various chains are connected in only one way: token holders on one chain can bridge over to any other chain where the project exists. When doing so, they take a proportional share of the project's surplus on the original chain with them to the new chain.
A project's projectIds are likely to be different on each chain.
A project can extend to new chains after its been deployed.
We call the component that bridges project tokens alongside their juicebox balance a Sucker.
Each chain has a JBSuckerRegistry that stores info about how local projects are connected to projects on other chains, through calls like JBSuckerRegistry.suckerPairsOf(...). This is also the contract where new suckers should be deployed from.
There currently are IJBSucker implementations for native bridges between Ethereum mainnet and Optimism, Arbitrum, and Base, as well as a CCIP version for bridging between the L2s and any number of other EVMs into the future.