I have a iPhone with a Canadian provider as well (Telus). In the account management settings on their website, I've turned off international data roaming. There is absolutely no possibility of incurring charges this way.

When travelling, I have purchased prepaid mifi mobile hotspots, kinda looks like a mobile but only one button. In Australia for example, they are about $100 for the device and it comes with 8gb of data. This is far less expensive then a day of international data roaming at $10 per mb. Connect ups to 8 devices so the laptop, kindle, iPhone and iPad are all connected.