Welch, 24, has been called in as a replacement for Luke Hume, who has suffered a leg fracture.
Dallas-born Welch has been playing for Connecticut Wildcats.
He said: “I can’t wait to represent the country it’s going to be a honour and an amazing experience.”
Welch moved to Warrington in 2003, and joined the Wolves’ youth academy under Paul Cullen.
He made his solitary appearance in 2008 against Castleford.
Meanwhile, the Tomahawks have announced the most capped player in their history, home grown rugby league pioneer Curtis Cunz, as their team ambassador.
Cunz will be the public face of the Tomahawks during the tour, attending all official functions.
He has also been nominated to the RLWC judiciary panel.