US to Canada isn't too hard, Canada Customs has a booklet. So likely US customs does too (maybe even their web site has it). You've got the added complication of California smog laws so you'll probably get more hassle from them then the feds.
Since everything in California was imported from the rest of the states, I'd try MG/British clubs in the state as their members would have dealt with the state hassles before bringing stuff from other states.
Has for how to get it there? Drive down the coast with the top down, that's the whole point of owning a British convertible!
