When i was in st thomas and in SJU i used my verizon plan. I didnt see the bill yet but i know that in both places it was free data and texting but calls were 1.99/min in STT and .69/min in SJU!
I used my google voice which is integrated in phone and dialed like a regular call. The only issue with that is that you cant call locally with that.
Can the canada plan also work for those locations?