Even if you keep the old AppleID established with the Canadian store you will eventually lose access to it as your billing information becomes invalid (won't verify). The iTunes Store in a country is intended only for use by that country's residents, and only while they are in the country. To use the iTunes Store in a country you need a credit card (or other card type if acceptable in a country) issued in that country, billed to an address in that country, and also be physically present in that country when using the store. You are also restricted to waiting 90 days between country changes.
E.g., "The iTunes Service is available to you only in the United States, its territories, and possessions. You agree not to use or attempt to use the iTunes Service from outside these locations. Apple may use technologies to verify your compliance." - http://www.apple.com/legal/itunes/us/terms.html#SERVICE - Same applies to pretty much all countries.
Yes, you will lose access to things you have purchased but then they should always be backed up anyway. As long as you have copies on your computer you will have them.
Do not set up a new AppleID. You can't transfer purhases between them or merge them later. It becomes a real nuisance when authorizing devices.
App Store Frequently Asked Questions (FAQ) - http://support.apple.com/kb/HT2001 when using iTunes --> "To change countries, scroll to the end of the iTunes Store home page and click the flag indicating the current country. To choose a different country, click the appropriate flag."
iOS: Changing the signed-in iTunes Store account - http://support.apple.com/kb/HT1311 - Change your iTunes Store country: "Sign in to the account for the iTunes Store region you'd like to use. Tap Settings > iTunes & App Stores > Apple ID: > View Apple ID > Country/Region."