This article should help explain how easy roam works.

Basically anytime you send a text, talk (incoming or out going), or use cellular data, you will activate easy roam for that day.  As long as you stay within your plan limits, you should not incur other charges.  If you have long distance add-ons they may not apply while roaming so long distance will be charged at full price.  With easy roam, you are able to call back to canada, and locally in the country you are travelling.  1800 toll free numbers are only for North america and if you are outside north america you will be charged a long distance toll.