They do allow either a stopover, or an open-jaw.
So, I was able to book in J, for 40,000 points YYZ-YYC-MIA... Because I wanted a stopover in YYZ, I couldn't do BOS-YYZ-YYC... However, if I could have done that, it would have been sweet.
I'll just use a different 15,000 award for that. Thanks for your help!