Shawcross won one cap for England as a substitute in a friendly defeat against Sweden two years ago, but has since been overlooked by Roy Hodgson.
The Chester-born Stoke captain grew up in Wales and has the option of playing for Chris Coleman's side, but has remained adamant that if he features at international level again then it will be for England.
Pulis knows all about the centre-back's ability after taking him to the Britannia Stadium from Manchester United and giving the 27-year-old the captain's armband.
And the Welshman has urged Shawcross to turn to Wales after being repeatedly snubbed by Hodgson.
"I'm convinced he should be in the England squad and if that's not going to happen then my attentions would be turned to crossing the border." he told The Sentinel.
"If England don't think he's good enough, Wales certainly do. I know that for a fact.
"He would be joining a Wales team with a genuine chance of qualifying for Euro 2016, so there's some big games to be had if he made that choice."
Pulis is in no doubt there is more to come from the defender and thinks he should remain at Stoke in order to continue his development.
"I still think his best years are ahead of him," the former Crystal Palace boss said.
"I'd be disappointed if Ryan thinks he's reached the top of his performance levels because he has still to reach his peak and should become better over the next four or five years.
"It's lovely that he is now recognised as a Stoke City player in an age when players are going from club to club.
"Yes, everybody has ambitions to play for a top-four club, but Ryan couldn't be at a better club than Stoke, for himself and his family.
"The supporters love him and he has so much respect in the dressing room.
"But he's earned that, it hasn't just happened."
