As long as you are in Canada, you are good to greet your fans and spread your goodwill anywhere at no charge, especially the US,
except for the following quote from Koodo NittyGritty:
Availability of service will vary by country and is subject to change without notice. Excludes premium messages and subscription-based messages. Picture messaging includes international picture messages sent and received within Canada. Picture messaging is not supported by BlackBerry smartphones that are not on the BlackBerry 10 operating system.
So for regular texting while you are in Canada, fine, but don't be a couch potato and text your vote to some premium number in the US while watching some iteration of someone's idol on TV or music infomercial.
If you are travelling in the US, your pre-paid phone will not work at all, so that settles that.