Moose Mobile does not currently have support for eSIMs.
An eSIM is not essential in order to get internet functionality on a smart watch. If you would like to use the mobile network with a smart watch, the best alternative is to sync the smart watch to your phone with a SIM inside.
E.g. the only time you would need an eSIM is if you wanted to leave your mobile phone at home and still receive calls and texts to your smart watch.