Forget about blending in. Any bike you take above 250cc will stand out. A KLR is a huge bike by Central American standards. Unless you own a KLR I would ride the bike you have and spend your money on having a fun trip. There are paved roads all the way to Panama. A big Harley looking Kwak cruiser will get a lot of attention, sure. But it will be lots of macho admiration. If anything you will get stopped at the roadblocks more often and asked how much it costs and how fast it goes, and kids will want you to let them sit on it and take their picture. That sort of thing. People in the rural villages will have the same awe and wonder that you would have if a Lamborghini Murcialago or some other car that costs more than you make in a few years came into your hometown in Ontario. You would be in awe. And if the owner got out and smiled it would be a conversation starter. You'd want to know how much it cost and how fast it could go where he was from and what he was doing in Ontario even if you were too shy to ask. And if he took your picture next to it so you could show your neighbors what a macho stud you are in your own imagination you'd be in hog heaven. We're all kids at heart. Latinos are no different. Young villagers getting their picture taken next to you and a big flash cruiser would be the equivalent of you getting your picture taken next to an astronaut standing in front of a space shuttle. Not a bad thing although it may get tedious after the 400th time.
The only downsides I can see are that you will have to be extremely careful going over speed bumps. I followed some fun riding Mexicans in Chiapas on cruisers and their technique was to slow down to a crawl and take the speed bumps at an oblique angle to avoid scraping their pipes too much. Also you will have a somewhat harder time finding secure parking at night. Many guest houses will let you ride into the lobby and park your bike for the night. Hard to believe I know but it's a normal practice. In populated areas it may take you slightly longer each evening to find a courtyard or other estacionamiento seguro (secure parking) for a large cruiser to easily fit in. Also I would recommend getting a bike cover to shroud your bike at night. It is amazing how well that keeps shy kids away from your bike. Out of sight, out of mind really works when it comes to big expensive bikes. Also it will limit your ability to visit villages down jeep trails and you will have to be careful going through road construction detours. But that's no different than Canada.
Have a fun trip!