"Back in the day", we did the two 7-nighters offered out of SJU on the CB. It was a great way to get an introduction to more islands. I like that both legs have a sea day at the end. We were able to fly N/S between YYZ and SJU at the time. I'm not sure if they had 10-nighters then which generally have more sea days. I hope this works out well for PCL.
Nowadays, we'd just be going tor a tropical escape, so PE suits as a jump point. It is true that cost-per-day to cruise was much less out of SJU and helps offset the higher flight cost.