Arfield, 28, was born in Scotland and earned the first of seven Canada caps in 2016, and Adekugbe returns to Vancouver from a year-long loan to Brighton and Hove Albion on June 30.
The pair join nine MLS players, two NASL player, and a USL player, with the rest of the group based outside North America.
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Notably, Orlando City players Will Johnson and Cyle Larin were not called up by coach Octavio Zambrano.
Goalkeepers: Maxime Crepeau (Montreal), Milan Borjan (MKS Korona Kielce), Jayson Leutwiler (Shrewsbury Town)
Defenders: Samuel Adekugbe (Brighton and Hove Albion), Fraser Aird, Manjrekar James (Vasas Budapest), Dejan Jakovic (New York Cosmos), Adam Straith (FC Edmonton), Steven Vitoria (Lechia Gdansk), Marcel de Jong (Vancouver Whitecaps)
Midfielders: Scott Arfield (Burnley), Patrice Bernier (Montreal), Alphonso Davies (Vancouver), Raheem Edwards (Toronto FC), Junior Hoilett (Cardiff City), Mark-Anthony Kaye (Louisville City FC), Anthony Jackson-Hamel (Montreal), Jonathan Osorio (Toronto), Michael Petrasso (QPR), Samuel Piette (CD Izarra), Russell Teibert (Vancouver)
Forwards: Lucas Cavallini (CA Penarol), Tosaint Ricketts (Toronto)