Dominion fleets could acquire their own carriers

Would Canada or Australia develop aircraft carriers if they retained their capital ships?

Possibly; a smaller Unicorn-like carrier or a transferred Courageous-class conversion is more plausible than an Ark Royal-sized ship.

A Canadian or Australian fleet with retained capital ships would have a stronger requirement for organic aviation. An Ark Royal-sized carrier is unlikely, but a Unicorn-like design is plausible. Britain might also transfer Courageous or Glorious while building more advanced carriers for itself. Ownership of one ship type creates a need for the institutions and balanced fleet required to operate it effectively.