Messaging Geographic Permissions generally work based on the country code of the destination phone number.
Assuming I have Canada and the USA enabled in my Geo Permissions, does the above mean—with the understanding that nothing is guaranteed here—I can send SMS to a Canadian mobile phone number anywhere in the world, or do I need to enable geo permissions for "Country X" for a Canadian mobile phone number to receive an SMS while that phone number is in Country X?
Only the country code of the destination matters, not the country in which this number is connected to the network.