Verizon is often acting like an evil megacorp, but in this case I'd say it's all your wife fault. The roaming rates are in the contract. Canadian telecoms may be charging Verizon a lot to use their networks.
I eventually found the rates buried on the verizon website several clicks deep through greyed out deemphasized links in the mifi data plan options. They're not available anywhere in her account information. They're also displayed in a hard-to-read run-on sentence style that mixes all countries together, not an easy to understand table. Verizon is clearly trying to hide this information in order to trick users into huge charges.
http://www.google.com/search?q=verizon+data+roaming+canada+r...
Here phone companies literally give someone unlimited credit to hang themselves. Add that to 45 day period before you know about the bill. Yeah, its stacked against you.