OK if you can plan & know your use ahead of time and budget accordingly. Same number and folks back home can still call you at local rates. Otherwise, about as much use as an American phone is in Canada.
Better off getting a SIM or Tracfone if you are going to be there for an extended period of time.
Koodo does have some discount Roaming plans for the USA and you can still add them. In the future you should add Roaming plans the day you leave for your trip into the USA. Otherwise you'll pay the pay per use charges.
@Carl did you not know what you were going to pay by using your phone down south? You are right, you can get a cheap phone in Phoenix, albeit with a different number, and find an outfit that's cheaper. Live long and prosper.
When you first arrive in the US you will have received a text message explaining what all those charges are. If you didn't add on a roaming plan, then youll be charged at the pay per use rates which are expensive.
After all the horror stories on the news from customers with other carriers getting $10000 roaming bills, it still baffles me why people still have these problems. Everyone knows roaming is expensive, but they still travel without a roaming plan and use their phone for everything.