No, there isn't a mechanism. I don't know whether they're going to check.... When people cross at the border, is Canada border security going to provide that data?
Basically, the return itself doesn't require any proof. It just asks, “Do you agree that you've been here 28 days?”
Every tax return is subject to audit. I don't know if the tax department is going to audit the one or two million of these it's going to get. I don't know. I'd have to defer that to the CRA to see how it's going to deal with that.