This is a bit of weird question. First of all, since you're Canadian, you know the advantages of having your child born in the United States -- it means that they have all the privileges within the United States that you do in Canada. No more, no less. If you think this is important, and that they need some sort of insurance against being forced to live in Canada, then go ahead and do it. It'll be expensive.
As for the disadvantages, your child will never have an RESP without huge bureaucratic and accounting hassles, and RRSPs and TFSAs will be tricky; they will spend their lives filing taxes twice and informing the US government about the contents of their Canadian bank accounts; they will have to maintain two valid passports to travel between the two countries (particularly expensive when young); and they will be exposed to any US legislation that affects U.S. citizens. Unless they live in the United States for some time as an adult, they will be unable to pass their citizenship on to their children.
I'm curious if you're doing this as a status symbol, or passport-collecting? Usually Canadians who want to work or study in the United States can manage that without being born there.
