Earlier quoted context omitted.
He presumably did not have access to the court's opinion before it was released, but he did have access to internal White House legal opinions before the tariffs were announced ("Mr. President this is illegal and very likely to be overturned by the courts"), and he obviously had access to the entire federal legal team during the court cases. I can't prove that there was any White House advisory memo before the tariff…
You’re piling speculation on speculation. First of all, there was no such memo saying the tariffs were “very likely to be overturned.” The Supreme Court decision was 7-3, with two Bush appointees voting to uphold the tariffs. The appellate court decision was 7-4, with two Obama appointees and two Bush appointees dissenting. Second of all, there is no evidence that this legal analysis was leaked to Cantor.
You're right that maybe there never was any internal memo, just thought this was funny.