If you are planning on going to Canada, data roaming does not work there. I have my LG-G5 phone and my wife's Iphone 7 both with International Roaming credit. Both phone can make and receive calls and send SMS text. Data is not available as well as MMS text. I made sure that data roaming is turned on for both phones but no success. We went to different part of Canada (Victoria, Van Couver, Calgary, Banff) and never got the data roaming to work.
Having no data is very inconvenient as we cannot set our GPS to search and go to our next destination, we have to look for establishment with WiFi in order to set our next destination.
So, if you are going to Canada or any other country outside of U.S. your best option is to buy a local SIM and use it for the time you are in that country.
Also, we found that we have to constantly have to re-start our phone in order for us to get cell signal. My LG-G5 keeps on getting the No USIM message while my wife's Iphone 7 is getting the invalid SIM message, when we restart the phone it connects to the cell tower and we can make calls and text.