My family has unlimited talk and text but my friend lives in Canada and the only way we have been communicating is online. If he gave me his Canadian number and we messaged would I be charged extra?
It does not, texting to Canada is included with your plan.
You may want to double check your plan/features, just in case you have an older one which may not have included Canada texting.
Texting to Canada was included in Nationwide plans and now the More Everything plan.