Can iPad 8th generation and Apple Watch series 3 connect?

You cannot directly pair ANY Watch with an iPad.

With that stated however, an Watch CAN be used with an iPad using the Fitness+ app.

Your iPad needs more that just the app.

Here are the requirements needed to use the Fitness+ app and Watch with a iPadOS compatible iPad.

Your iPad needs to be updated to the latest iPadOS 14.3 or later.

You need a compatible Watch ( series 3 or later ) updated to its latest watchOS version.

No options

The Fitness+ app will ask to automatically link the Watch to your iPad/ Fitness+ app, after the download of the Fitness+ app from the iOS App Store.

See the iPad/iPhone instructions here below.

How to start a workout.

Tap the link below.

https://support.apple.com/en-us/HT211923

Also, make sure all connected Apple devices are using the same Apple ID/password account information.

This is the ONLY current instance of being able to use an Watch with any iPadOS/Fitness+ compatible iPad.

In addition, there is no TV mirroring of the  Fitness+ app, using iPad, currently.

Currently there is no direct AirPlay/screen mirroring from an iPad to any other compatible smart TV or smart device using AirPlay2.

Apple, currently has ONLY made the mirroring/AirPlay 2 feature available to owners/users of an actual Apple TV box.

Best of Luck to You!

No, a Apple Watch cannot connect to a iPad as it is made for iPhones (iPhone 6 - iPhone 12 Plus) The app used to pair your Apple Watch with your device is not available on iPads so it is impossible to do so.