1

You are very unlikely to get any persons on these boards who have experience renting a sailboat and captain for 3 months and taking a 6,000+ mile journey as most of the active participants on this particular branch are more geared to budget travel and taking public transport options. You would be much more likely to get a serious response to your inquiry on a site like Cruisers Forum that specializes in sailing and boating or contact a sailing charter company like The Moorings. Also be sure to post it on the “Life on the Ocean” branch of Thorn Tree (didn’t look like you had done that yet).
Having said all that, based on my very rudimentary knowledge of sailing but pretty extensive knowledge of geography and travel in the Caribbean and Central/North America, your plan seems very unrealistic. Have you charted out the incredible distances you are contemplating? For example, Barbados to Panama City is about 1,400 miles (and if you plan on sailing around the Caribbean, add hundreds or even thousands more in mileage), onward to the Galapagos is another 1,000 miles (sailing across the open sea; if you hug the S. American coastline as long as you can you are still talking about around 600 miles offshore from the coast of mainland Ecuador + another several hundred miles down the coast from Panama) and then Galapagos to Vancouver is another 4,000 miles or more. In addition, for your rental boat to return to its home base in the Caribbean, it will take a return trip of another 4 – 5 thousand miles that you will have to compensate the charter company for. So right there you are talking about ten or eleven thousand miles. Even at 100 miles a day, that is 100 travel days of pretty much non-stop sailing (although I realize the last 40 or so days would be without you onboard as the boat returns to the Caribbean). Not sure what you are expecting in terms of cost, but it is going to be a pretty astronomical amount. Going through the Panama Canal isn’t exactly cheap either (and not quite as exciting after a few hours as it may sound, though Panama is a fantastic place to visit).
Also, your search for a captain “that knows these areas well” is probably very unrealistic given the huge diversity of these locations and distances between them (this would not exactly be a popular itinerary).
One of my biggest concerns with this itinerary (assuming costs were no issue), would be endless hours at sea in a 50 – 60 ft. boat. For example, sailing from Panama to the Galapagos will take you a good week to 10 days of sailing in the open seas each way, out of sight of land.
My recommendation would be to just focus on the Caribbean area. Islands are relatively close together so you will never be out on the open seas for days on end, and there are tons of interesting and beautiful places to visit. In 3 months you could comfortably sail the length of island chains. Also, you shouldn’t have a huge problem finding a boat and captain for that sort of thing. If you want to experience some different areas like the Galapagos or the Sea of Cortez, you could spend 2 months sailing around the Caribbean and then just fly to your more distant destinations and charter a sailboat there for a few days to visit the area in depth.
Let us know how this works out. Would love to hear what kind of a cost estimate you get if you could find someone to quote you a price 

2

Have you posted this on LP's Sailing branch? Might get more responses there.

3

Sorry, hadn't read mgtraveler's wonderful, well-thought response. I, too, am curious about your cost estimates.
On another note-- there is a sailboat for sale in Port Antonio. It's been around the world with a family of 4 onboard for 2 yrs. Contatc the Port Antonio, JA, Errol Flynn Marina.