I think you can REGISTER the boat in Canada (takes a few weeks and a few $ too), and if you are not importing the boat you won't have to pay the taxes. You will have to pay your sales taxes somewhere (broker may have a waiver for him if you are not paying the the state you purchased it) - and if CA is a good rate for you - go ahead and do that. Sounds sensible. Also if you are Canadian registered, Cuba will never be a problem :-)
I paid VA tax but did not register the boat in VA, it was not easy to find the right forms, but an email to the agency that handles it got a quick reply. You can email the CA folks and just check they won't have any issue with excepting your money (How could they say no?).
I know of another boat purchased in the USA by Canadians "Slapdash" their report
says "In the end we had to resign ourselves to the maddening (and expensive) bureaucracy of our home and native land. The process is so tortuous that we actually had to hire a professional that specializes solely in registering non-Canadian boats."
. But even that did not go smoothly. Along with other frustrations imposed by the Canadian guys - special bills of sale, and notarized sellers signatures. So be prepared for a few headaches, give yourself plenty of time to get the process completed before you plan on leaving the states with the boat. See Slapdash posts of 19th and 26th September 2007
Good luck, and have fun!