All seasons and episodes, dub and sub, can be found in the linked Google Drive folder. It is fairly easy to navigate, generally of good quality, and you can adjust the speed.
All seasons and episodes, dub and sub, are also located here. Compared to the Drive folder, it can be difficult to navigate, and so the link actually connects to a Google Doc to make this easier. On the plus side, Google Photos has a fun comments section and like feature which is not available for Drive.
There are many anime streaming sites available, most don't have the entire collection of Hetalia, and many are frequently taken down. However, using the linked Reddit Megathread, try the "GOATs" listed among the many anime sites, and hopefully, you'll get lucky. Make sure to use an adblocker and don't trust any pop-ups, including those that say you have a virus (those are secretly ads for virus cleaners).
Here is also a Google Sheet that contains a descriptive list of each episode and the appearing characters. It's made for if you need to find scenes/screencaps of certain characters or want to remember which episode had that one scene.
@hetascanlations on Tumblr
The main fangroup that's been translating Hetalia for 9 years and is often considered by fans to be the "official" translation, or at least the MOST official. Their Tumblr page is where you can get the fastest updates from them, but Tumblr pages can be a bit hard to navigate, so their chapters are also available on...
This page is managed by one of the Hetascans members and contains not only the translated chapters from the manga volumes, but also the original webcomic, and hundreds of other archived blog posts from Hima. It has a search bar to look for certain characters.
Mangadex Comick.io (and other manga reading sites)
Hetascans had also uploaded most of their chapters on Mangadex, which has a fairly nice interface and easy navigation. Unfortuately, MangaDex got DMCA'd and all the chapters are now gone... Fortunately, sites that auto-reposted from Mangadex such as comick.io still have them (for now...) Other sites like mangago.me also have some of the old work too.
@north_italia on Instagram
This account posts frequently whenever there is a new chapter, illustration, musical, merchandise and more. To get the most and fastest updates from them and mutable notifications, they hold a "broadcast channel" (like a fancy one-sided group chat where you can only react) with over 400 members which you may request to join.