Hi there.
As soon as you leave Canada your device will automatically switch onto one of the wireless network providers in your new destination. A text message to Canada will cost you about $0.75 (it depends on which plan you use).
You can buy $40 European Talk & Text Travel Pack 15 Minutes & 100 Sent Text or another one with more minutes and texts.
How-to send SMS when in roaming:
1) Save all numbers in your device (or some of them) with "+" "1" area code and 7-digit phone number, for example, +14165551234. Then you can simply dial from your phone's address book.
2) Otherwise, you need to dial "+" plus country code, area code and 7-digit wireless number to send sms or make a call.