Getting J class fixed mileage/classic awards is difficult - unless one has SuperElite status. I guess if one has millions of Aeroplan miles in one's account, and no status - one can use the higher redemption rates of market Aeroplan awards in booking J class seats.

The one advantage to flying in the international configuration J class with AC is the "open pods" with flat bed seats. To my knowledge, no other North American airline at least in business class (I do not know about first class) offers such a benefit in J class.