Don't tell us that "I've configured X correctly", if you did everything correctly you wouldn't be there. Please add more information to the question: What OS? What compiler are you using, how did you install it? How exactly did you install OpenCV and Cuda? Show your config files if you have them:
c_cpp_properties.json, tasks.json, etc. Can you successfully compile your program in the terminal, or is it only intellisense that's complaining? Those two need to be configured separately.