I currently use directbet.eu but they only offer a few racetracks to bet on and there are very few north american tracks to wager on and you only can bet w/p/s. If there are any other sites that offer better horse racing please post names of sites thanks.
There doesn't seem to be any other good site offering Horse racing. Maybe you can try on one of the fiat sites .
You also have https://nitrogensports.eu , but not many horse bets
I leave my referral here if you are interested https://nitrogensports.eu/r/390925