OK, I can see a line close to the end that says:
extern MCP_CAN CAN;
But I'm wondering if the "extern" keyword is making it think that the object is actually going to be created somewhere else.
You could try adding this to your sketch before void setup(), and leaving the header file as it is.
MCP_CAN CAN;
By the way, it's better when posting code in the forum to use the code tags - there is a button marked "#" above the row of smileys. It makes the posts easier to read 
All the best
Ray