If your phone is compatible and unlocked you can bring your own phone to Koodo and get a plan. You will need a Koodo sim card.
You can keep your existing number. When you sign up for Koodo service, bring in your current service provider's bill/ account number and tell them that you want to port your number.(Don't cancel your current service until you have done this)
You are required a credit check if you want to activate the monthly plan.