I want build a wallet which manages multiple coins and I'm looking for a website which provides APIs for transacting to different blockchains.
In short No, because what what you're essentially asking for is a crypto exchange mechanism.
What you're probably looking for is an API to create wallet for multiple coins of a variety of blockchain and have your backend to instantiate these wallets and make pair exchanges. However i do not see why your product would be any different from the API provider.
