Some Ideas
Try Expedia.ca - round trips you need dates but Air Jamaica flies one way for $219.06 to $240 CDN PAP to SDQ - sooooo.....nearly $500 with 2 one ways.
It may be less Aeroplan points to go YYZ to MIA. Then buy a R/T MIA to SDQ on AA or MX ( or, perish the thought, Aeromar) , often quite good deals depending on when you go and how long you stay. I would think much less Aeroplan points to redeem to get to MIA as well so you save some there for later travel. (True 40,000 to PAP , 25,000 to MIA - intersting AA only uses 30,000 from Toronto to SDQ)
Never having been to Haiti, nor wanting to (the sentiment of many people here I think) , I would think it must be a rather poor choice of connecting airports as well.
Since Mexicana is Star Alliance and they fly MIA to SDQ can't you do YYZ to SDQ on them ( undoubtedly they would code share YYZ to MIA on AC anyway).