Getting a bit off topic but I can confirm that it happens to Americans coming into Canada too.
A good friend of mine (40-something year old Canadian) was engaged to a 40-something year old American (not that it really matters but just wanted to mention that this happened to older professionals not just some high school / college kids backpacking or something ...). Before they were married, they decided to come live together in Canada since that's what they were going to do once married so she resigned from her job, packed up her things and they drove through CND Border together. She was denied entry and was banned indefinitely from Canada. They got married a few months later but I think it still took about 18 months (might have been more - I have ask him exactly how long) until they were able to get the ban lifted she was able to come to Canada. During that time, she wasn't even able to come for a short visit even if her husband lived in Canada. The worst part is that they were not able to get any idea of the timeline ... they didn't know if it was going to take 3 months or 3 years so she didn't know if she should look for work, etc (I think she end up doing work that she could do from home in the US or from Canada)
And this is for someone who lives in Ottawa and was able to deal in person with all the red tape and hoops to get this resolved.