I get rather passionate about digicam discussions so I'll try and tone it down.
Questions:
Did you like your Canon? Is it missing any features you want?
Do you print your shots or just post them to a web site?
If you print, do you print really big enlargements?
Don't fall into the megapixel trap. I'm with Paul on this one, for the vast majority of us, 4-5 megapixels is more than enough. Tossing pics up to a web site or printing anything under 8x12 and a 4mp camera is more than enough. I'd spend my money on a camera with a quality lens and with features you'll use.
My cameras are 3mp (Olympus and Minolta) and I get extremely good shots with them, especially the Olympus. I have enlarged prints up to 30x20 with little noticable hit in quality. The difference is the lens is very good on the Olympus so the shots are very clear. The Oly I have is a bit bigger than what you're looking for though.
If you liked your Canon then buy the same model. It'll be inexpensive, you know how it works, and you've likely invested in a CF card for it. Iif you snorkel or dive look at the cost of an underwater housing. They typically run for about the same price but you might be able to get it and another A40 for what you want to spend. Or, use the money you save on an excursion to Chichen Itza while on your trip.
Besides The Camera Store, visit Saneal and Vistek just to get some other ideas of what's out there. For price comparisons go to
www.henrys.com. They are out of Ontario but you'll get an idea of cost. Also check ebay as there are camera stores which sell new items on there for less cost than in store. I bought my Minolta and underwater housing through ebay.