And once again, I'll say that the responses you get vary from location to location. Canadian customs has very little to do with it, other than collecting the GST, and possibly PST depending on your province. However, it is US law that says all wildlife (yes, this includes CB herps) leaving the US must be inspected by USFWS. If you leave the US without doing this, you've broken US law, and under WAPRIITA, you've also then broken Canadian law.
Now this doesn't mean someone will show up at your door the next day. But you have broken the law, and it certainly could come back to haunt you.
So, to do it legally, contact USFWS at the border crossing nearest you that will do inspections. Not all of them do. Some offices will inspect you without a fee if you only have a couple of things for personal use. Others will follow the official rule that you must buy an import/export license for $50 (good for one year) and pay $55 for an inspection. All of this still assumes no CITES listed stuff.
Oh yeah, Canadian laws make it very tough to import turtles. But that's a whole separate issue.