I would like to know how can I use the MetaTrader5 (no broker branding) as a platform on my PC to run my algorithm and to communicate with more/one broker`s API?
What Im looking is to avoid building a .NET code for "everything" and instead only to build the trading algo.
Why don't you implement your algorithm with MQL5?
With MT5 you can connect independently to any broker compatible with MT5, just changing the login and server connection, so choose a broker compatible with MT5 solve your problem.
But if you are thinking of developing an universal algorithm using brokers that are not compatible with MT5 (but provides a connection API), please confirm this and pass more details of your idea and project, so we can try address a solution.