Depends on our location.
If you're outside of the USA, you could consider a broker like Pepperstone who offers cTrader (platform with C# API,):
https://pepperstone.com/en-au/trading-platforms/platforms/ctrader/
That would mean you're running a bridge of some sort again, but integration can be a lot more seamless / fast given the C# environment.
However, if you'd rather there's always a FIX option, which would provide much better connectivity (speed/latency/etc) and be super lean without the need for a bridge beyond what agent code you write to connect:
https://pepperstone.com/en-au/trading-platforms/tools/api-trading/
(Often FIX won't come with historical data pulls and just be real time streaming only, so you might need to work in a historical feed.. but talk to your vendor of choice anyway to see what they offer.)
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Another option would be Interactive Brokers, who has a decent suite of APIs that support many languages, and they also have FIX but that comes with a monthly fee for connectivity. Only drawback is the minimum commission charges for FX trades on IB, making deals sub 50k notional kinda costly relative to other brokers. If your average deal size is much larger than this, then it's not even a problem.
https://www.interactivebrokers.com/en/index.php?f=5041
Interactive Brokers is also a sponsor on this forum. I use them myself for options trading and think they are solid.
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I'm not sure what the best offering is if you're a US resident as Interactive Brokers has hefty restrictions for Forex in the USA (imposed by regulators, not their fault,) and most on-shore FX brokers in the USA aren't very compelling... perhaps using Oanda's v20 API might be worth a look.
Unless of course you're working with a decent chunk of capital and will be doing yards of volume... then you can look at some prime / institutional broker options in the USA such as Intl FC Stone:
https://www.intlfcstone.com/Commodities/Currencies/
However, you start to get into relationship based pricing and execution environments there... and they don't really cater to small traders.