Let's be totally clear here; if the government is interested in you, your choice of computer platform matters very little in terms of hiding information about your life.
It is also worth noting that the USA is not the only country collecting data on US persons (and everyone else.)
The question is not, does the USA know about you, the question is really, how many governments know all about you and how does that information manifest in your life?
Yes, and its probably fair to assume that Apple and/or the government can access any of your files on your devices or in the cloud. My suggestion is not to use any "provider." Use free software, and keep your data locally on encrypted drives.
For the vast majority of people, the hassle simply isn't worth it, especially when the massive reduction in convenience is paired with basically no improvement in security.