Look at the list of typical opponents. If you aren't a very good driver, pick a car that has higher PP than them. If you are an average driver, pick a car with the same PP. and if you are a good driver or want a challenge, pick a lower PP car 👍
These races at the Pro level are not exactly demanding and the AI is not very aggressive so a good road car could win them but keep in mind you are going up against thoroughbred race cars so whatever you choose you'll need to be pretty good with it and your car will need good top speed. I have just run a minimally tuned Audi R8 5.2 and won very easily so a road car with a tune is certainly possible.