Oh, good question. 1st, you might want to check with your current provider. It might include Canada for free (some include Canada and Mexico for free...others don't. Worth checking). But if you need it, I would buy the eSim before leaving the US, then activate it maybe the day before you leave (in the app it will give you activation steps for setting the eSim up on your phone). Just make sure your phone accepts eSims. If it's a new Samsung/iPhone made in the last 2-3 years you should be fine. But if it's an older model or different brand, it's a good idea to double-check.