Generally, no. However, the Canada-US plan may have an exit penalty, and if you received any special considerations beyond the phone payment, there may be other costs. I suggest reviewing your contract, as they differ from time to time.
Check my contract, clearly says only the device balance. So another question, what happens to my 12 dollar tablet plan that shares data with the phones that are leaving. Does it just get canceled or will they automatically bump it up to one of their height priced data only plans?