On the International Roaming: Rates and Coverage page we can find your answer.

Look under International CDMA Roaming Text Messaging Rates.

You'll see it says: While IN Canada you are charged the domestic rate or per your plan. Meaning messages are deducted from your plan unless unlimited or .20/message if you're not paying for a text plan at all. 

So if either one of you continues to roam in Canada, your best bet is using text, not voice.