Given the arrays:
int canvas[10][10];
int addon[10][10];
Where all the values range from 0 - 100, what is the fastest way in C++ to add
You can't do anything faster than loops in just C++. You would need to use some platform specific vector instructions. That is, you would need to go down to the assembly language level. However, there are some C++ libraries that try to do this for you, so you can write at a high level and have the library take care of doing the low level SIMD work that is appropriate for whatever architecture you are targetting with your compiler.
MacSTL is a library that you might want to look at. It was originally a Macintosh specific library, but it is cross platform now. See their home page for more info.