An ISP owns a pool of IP addresses. Most ISPs use dynamic address allocation, so that they do not need exactly the same number of addresses as they have customers. What that means is you may be given an address (for an agreed-upon amount of time, after which your computer must ask for an address again -- and it may get the same one or a different one), but when you shut down your computer, you're releasing that address back to the ISP. If an influx of other customers such as yourself demand enough addresses, the one you had may be doled out to someone else; that's why your address may change.
IP addresses are pretty geographically stable, so migrating from Brampton to Downtown TO, you would very likely change IP addresses (unless, as previously mentioned you pay for a static IP address and you are staying with the same provider).
