We are going to Canada from the USA.?

Anytime you are attached to wifi you should not be incurring roaming charges. Roaming charges are incurred when you are streaming data through a data (i.e. cell phone type) connection. Some of those "portable" hot spots that you can buy to give you a secure link do this. In this case you are not connected to a wifi source so you would be charged. if you connect to a wifi through your tablet there should be no charges. If you have a data plan for your tablet you can always disable data but keep your wifi connection turned on (we do this and have never had roaming data charges). This cannot be done in airplane mode of course.

WiFi is handled by a local data router in a restaurant or someone's home. It doesn't go through the phone provider, so it can't incur roaming charges. You just have to be in range of a WiFi hotspot that lets you get net access.

If you use 1G, 2G or 3G wireless data, that's not the same thing as WiFi. Then, you're using the cellular signals to connect to the net, and you're responsible for the connect charges. Crossing the border into Canada, or even walking too close to the border will result in roaming charges if you try to access the net that way.

wifi is free most places

Probably but make sure you put your skis on the roof - even if it's mid August .......................

No. go by time machine instead.