We were up north in Canada last summer. T-Mobile month to month phones. No charge data and txt but $.20 a minute voice. Service was thru Rogers Wireless back into the T-Mobile network. Good 3G service but we stayed fairly close to the Trans Canada Highway in the area of the Great Lakes. Didn't talk much but a lot of email, txt messages and Facebook with family and friends.
T-Mobile based phones interface on the same standard as ATT (GSM) which is a bit more prevenient than the Verizon based phones (CDMA) for international service outside of North America.
If the phones you have now are unlocked a prepaid SIM is what you can try. You can also go with a month to month service with a service provider that has the free international rates such as what I got from T-Mobile. The key is you phones need to be unlocked so you can use any service provided the phone's hardware will work with.