Regarding the long distance add ons: Are these minutes and texts within the country you are visiting, or the country your phone is registered in? In addition, are zones 1 and 2 also $5 and $10 for 20mB, or 1mB? Is there a way to set it so it will not use any data once this amount is used?
Long-distance refers to when you call from Canada. Roaming refers to when you call from outside Canada.
I assume that you're talking about roaming.
These rates are in place no matter whom you call or who calls you. You can disable data roaming in your phone's settings (or disable data altogether). As for limiting data after the threshold, many phones will let you do that. However, it may not be 100% accurate and cause an overage.