Ian,
How on Earth did you get that troopy up to 3500 kgs? That is 7716 lbs in real weight- that is massively heavy. My HJ47 with skids, high roof, camper interior, winch, roof rack and full tanks 'only' weighed in at 6800 lbs on the scales in New Mexico.
At any rate, I agree with malcb- a Toyota frame can handle the weight. You just might notice more wear in things like bushings, bearings, shocks, spings, brakes, etc. Depending how pedantic the countries you are travelling to/through are, there may be an issue with whether you will be allowed on the road or not, but I doubt it. Certainly in Australia, Big Brother would have a thing or three to say. But given you are going through Afrika and up South America into the US, I would not be too worried about anyone stopping you at the border for being over GVW.
As for Canada when you go to register it- I don't know what they will say. However, I'm sure you can get the weight down by removing a few select items before inspection.
Just make certain that you are happy with the efficacy of the brakes.
Cheers,
Josh