Impossible in the states? Not exactly.
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.