Hello Ross, I am not an expert, but I did in the end buy the iPad 2 with mini-sim card (mobile comms like celphones have). I find it useful but I usually have the roaming data switched off to avoid huge bills by mistake. You can always switch it on if you really need it (which is the power of the feature). Practically it is too expensive to use on a routine basis when roaming.... Would advise you to buy a GPS based system only like Garmin or TomTom if coverage in your area is good. Should be.
What we have here in the Netherlands is a contract that has unlimted data roaming. the deal is more expensive and I would not recommend it for everyone. That might be available for you too - don;t know.
However, given the distances in canada, I would not want to rely on deluular data networks for navigation. Apart from being more expensive, cellular data network may also have more service disruption than a dedicates GPS system which in the US and Canada can be quite inexpensive (don;t need top of the range and hunt for offers).
If you regularly tavel long distances, I would recommend you consider a SPOT satelite system that allows selected others to track your progress. You can also press a help button and this sends a message via satelite to your chosen firend(s) or family with you exact gps location. It also has an SOS button which would alert the rescue services. The latest systems also allw you to send short text messages to help with comms. It is not as cheap and not a naviation system (its ony for tracking). But we used it in the US for adventure trips and later also in North Africa in the desert.... so just a though.
Back to the iPad, it is a great and extrememly versatile device which I would recommend you would us e to download maps before you leave home and use them to keep an overview of where you are is the dedicated GPS navigation system does not place you in the big picture.
The Ipad can also be used to exchange important information if you are in trouble and you can share you position if cell comms is possible,
Not sure this helps but just in case.
Best of luck, Floor