Can I still use the Apple Watch GPS + Cellular even if I never connect it to my cellular provider and used it as a regular Apple Watch GPS?

Yes, but then there's no point in going for the cellular version.

If you are never going to use the cellular options then just go for the GPS only version as it is cheaper and will do the same things.

Hi

Yes, you can.

Without a compatible service plan from a supported carrier, you will not be able to use the built-in cellular feature.

However, Apple Watch Series 3 (GPS + Cellular) models can still be paired, set up and used for other features without activating the cellular feature, offering the same functionality as GPS-only models. The cellular feature can be enabled later, if and when you are using a compatible service plan on your iPhone.

Some differences between Apple Watch Series 3 (GPS) and (GPS + Cellular) models that you may find it helpful to note include that Apple Watch Series 3 (GPS + Cellular) models:

• Have double the storage capacity of Series 3 GPS-only models.
• Have a ceramic back (vs a composite back for GPS-only models).
• Include options for Stainless Steel and Space Black Stainless Steel cases (all GPS-only models are aluminium).
• Stainless Steel and ceramic (Edition) case models also have a sapphire crystal (vs Ion-X Glass).

Note that Apple Watch Series 3 (GPS + Cellular) requires an iPhone 6 or newer model of iPhone running the latest version of iOS (vs GPS-only models, which require an iPhone 5s or newer model):

Set up your Apple Watch - Apple Support

More information:

Buy Apple Watch Series 3 - Apple

Apple Watch - Compare - Apple

You're welcome.