There are a number of choices, depending on what you're trying to accomplish.

Two that come to mind are CoinAPI and Apifiny Connect.

• CoinAPI is a pure connection solution
• Apifiny Connect seems to have what you may be looking for. I'm trading on 5 out of something like 20 exchanges. They all have colocation which they gave me for free, but I'm not sure if that was a special offer. We're using the FIX API. I'd check them both out, depending on what you need. My fees are lower with them than on the exchanges, too.
  

From your post, it seems that you want one account. I really have only one account. And had only one onboarding.

You really have to check out the sites and read carefully to understand what they're offering and what you'll still need to source on your own.