If I am vacationing in the United States and want send text messages to Canada, are there any roaming fees if I am connected to the hotel WIFI in the US?
Yes there will be roaming fees for sending SMS from the US to Canada unless you have a plan that includes it. SMS text uses the cellular network and does not use WiFi. There are other messaging systems, like any of the popular social network platforms, that uses whatever Internet connection your device is on so those will use WiFi if that's how your device is connected. Those will also incur roaming data costs if your device is not connected to WiFi.
See this for travel options:
Difficult to say without knowing what your mobility plan is. You can always turn off roaming to ensure that it's not being used.