Pixel will have a lot better camera and will get quickest and latest updates for 3 years. Will be snappy due to stock Android and battery timing is great but looks bland. Also the cost is not nearly as powerful as the k20 pro's sd 855.
The redmi looks a lot better has a bigger screen and probably will have better battery times but it's a Chinese phone so your data being sent to our overlords in China is a big risk. Software updates i have no idea about as never used a mi product.
I'd recommend first checking what the tax will be on the k20 pro and then decide.
Btw what are you getting the 3a for?
Edit: I see you've mentioned that you don't play games then you should go for a pixel 3a.