No need to change Can $'s to US $'s at all. Just bring Canadian and change directly to Ja $'s. As well, do your buying in Ja $'s.
It'll be easier for the people you buy from and in the long run, cheaper too! We always bring travellers cheques and exchange at Cambio or Scotia Bank. Peace of mind in not having hundreds or even thousands of Can $'s in cash. This all works best for us!

Peace
Elvino