I brought my Catalina 270 from Missouri to Ontario (I know, the opposite direction) without any trouble or problems. The main point, though, was that i hired a customs broker. This was the best $250 spent on that purchase (maybe after the $500 on the survey). The driver who moved my boat spent under 10 min with customs; according to him, it was the easiest border crossing ever (and he does it for living).
I shipped using uShip. Eventually it worked, but I had all kinds of problems with the first company i selected (they were crooks). But the second time (good it wasn't the third

-)) was a charm and it worked great.
Andrews always has good reviews; I never heard of anyone complaining. However, they are not cheap.
Moving a boat across the border is not a rocket science; however, you MUST have all documents in order. Also be aware that even though the customs officers work for the same "company" and are, theoretically, bound by the same rules and laws, in practice, the rules are (or at least can be) different at different crossings. This is where the customs broker would earn his keep.
Good luck