apple watch series 3 works on metro pcs?

Hi

Apple advises that new carriers are being added for Apple Watch Series 3 (GPS+ Cellular) all the time.

Apple's list of supported carriers is linked below. Note that MetroPCS is not currently listed and that prepaid plans are also not currently supported:

Apple Watch - Carriers - Apple

I suggest that you contact MetroPCS to ask whether they offer or intend to offer service plans for iPhone that include support for the built-in cellular feature on Apple Watch Series 3 (GPS+ Cellular).

No, the watch only works with the major carriers that are available at the moment. You can click here to see a list of supported providers. MetroPCS does not support the Apple Watch.