You will need to get either one of the US roaming add ons http://help.koodomobile.com/Portals/0... or get your phone unlocked and get a prepaid sim in the US. (some examples would be t-mobile or roam mobility)
Examples of 3rd party services for unlocking your phone are cellunlocker.net or GSMliberty. If you have an iphone, getting your phone unlocked by koodo for $35 is much cheaper.
The unlimited texting on your plan is only for when you're actually physically in Canada.