US to Patagonia than up east coast Brazil WHICH BIKE!?
 

I am looking for a medium size bike that will offer a minimum of comfort and it's not impossible to find replacement parts in Central/South America! Through what I already researched on this forum I am leaning towards the KLR 650 or the V-Strom 650. What's your guys opinion?

Any bike will work and has. 50cc on up have been used to ride the world. I like the DL650 has road manners of a bigger touring bike (with a little work) and much less buzzing than the KLR. But the KLR is chaper works better in the dirt, parts may be easer to find as well.

If you start worrying too much about replacement parts in Central/South America the only true option you gonna have is a Honda CG 125.
If I had to choose a bike for this kind of trip my preferred options would be a KLR 650, XT660 or DR650, but in Brazil find replacement parts for the KLR and DR could be very difficult because none of those bike have been available for sale in the Brazilian market.