@CC11111111111 yes you can use your plan in both Canada and the US calls and data. Nothing extra needed.
Can be tricky to get connected sometimes. You have a VoLTE enabled phone?
You woukd need to put your hone to 4G/LTE and connect to T-Mobile or AT&T.
If calls still don't work, put your phone to 2G and connect to T-Mobile.
Ensure you turn on data roaming.
Sometimes after doing thus might have to restart phone.
