I've had a look at a few US based RV hire websites, and they all seem to say the same thing. That is, for normal sized RVs you need to be over 21, you need to have held your license for over a year, and for Europeans you need an International Driving Permit if your license isn't in English (which I guess your Belgian one won't be). Very large RVs, and those with air brakes seem to be different though.
I did see a few discussions suggesting that you may wish to take your C1 course (the license class needed to drive large RVs in Europe). The main reason for that is to ensure you're happy and safe driving a large vehicle. It'll also have the bonus that if you like RVing, you can continue doing it when you get home!
One slight wrinkle is that licensing in the US is handled state by state, and in Canada province by province too.
The best advice seems to be to ring up the hire car company you're planning to use, and ask them. It's not impossible that their insurance will have stricter requirements than the legal minimum, so that may be the limiting factor anyway. Most of the big companies should be used to visiting Europeans, so ask them and see!