EC2 is infrastructure only. Its a little bit like saying can i use letsencrypt with HyperV, XenServer or VSphere. The question is fundamentally wrong as LetsEncrypt certificates are usually used by Applications such as web servers etc to secure communications
So the question becomes what is your technology stack (e.g. LAMP, LEMP, etc)
What version of Linux + what web server + wordpress
there are a couple of Wordpress Plugin
Seems someone has written a guide on implementing EC2 with LE. However, EC2 has its own free certificate.
It’s not EC2 its AWS (Amazon Web Services). You need to differentiate between EC2 (a infrastructure service), AWS, etc.
Sorry to be lecture like but it’s important to understand these concepts as they will save you time