Air Canada and Air Jamaica have historic ties too, as AC was the airline which worked with the Jamaican Government to form JM back in 1968 out of a former BWIA nest of operations there. BWIA itself was also instrumental as some of its planes were operated in conjunction with JM until the latter got its own aircraft.
So, the AC/JM joint effort into YYZ not only makes economic sense but is also a means of continuing the good ties between the 2 carriers. JM in fact displays that codeshare on its route map (check www.airjamaica.com).
Hop to it, fly for life!