Is it possible to replace a device on existing line with Note20Ultra bought from Samsung.com?

I have an existing line, with a Note 9 512GB BYOD. I also have a Samsung Financing account and would like to use it to purchase a new phone, Note 20 Ultra 512GB. Two questions. First, do I purchase an unlocked phone, or a Verizon phone? and Second, can I purchase the phone from Samsung.com directly and activate it on the existing line to replace my note 9?