Texts to and from Canadian 10-digit numbers are considered domestic, and are included in your unlimited texting plan, no extra fees. CALLING the number WILL result in international calling charges, but texting is part of the plan. My daughter texts to friends in Canada quite often and we see no additional charges; the texts are just counted with all our other usage.
As SuzyQ stated in her posting, texting from the US to Canada is considered as a domestic text and is included in the text message package that you are subscribed to. For more information on international text messaging to other countries, I have posted a link for your review. Please see below: