As I said in another post, it's not the checkpoints that are not legal in the US - it's random checkpoints that have been ruled unconstitutional. As long as the police can show that checkpoints are not random (e.g. stopping every fourth car) and that they aren't profiling (e.g. stopping only import "tuner" cars), they meet the requirements and can stop motorists without prior probable cause.
In Canada there is no such ruling - they can just stop whatever car happens to be next after they finish with a previous one.
Here in California, when a checkpoint is set up, the cops stop EVERY car. Technically, it's legal to not stop, or to take a turn to avoid it, but anyone who does that WILL get chased down and stopped. Their justification then is that you avoided a checkpoint! Naturally, drivers will be put through the wringer at that point.
It's quite common here for the police to publish the results of local DUI checkpoints. Typically, it turns out that out of 1,000-1,500 cars detained, they get one to three DUI arrests. Sounds pretty ^&%! random (and completely ineffective) to me.