@Hobbayne No because you can only use your Smarty plan data either in the UK or for EU Roaming.
Any Roaming in the USA will need an add on to pay for it - check out the Price Guide, specifically pages 18 to 20.
You will see that data is charged at 10p per Megabyte in the USA - yes, that is £102.40p per Gigabyte!!!
If you need data over there other than via freebie wifi, consider a local sim or else an Esim (if the iPad will accept it - usually wifi + cellular models post 2020)
