David,
Staying out of 'the pitfalls of guiding as a career' stuff:
Whether you can operate a guide business year round depends primarily on where you are.
If you can be mobile, try to select a spot that has good fishig all year, has enough 'stuff to see' (natural or manmade-not just a 'fishing' spot, but something for the rest of the family to do as well) in the area so that folks will be coming there all year, and is enough well known for it's fishing that fishermen will be looking for a guide when they are in the area.
Don't be surprised that will be LOTS of guides in any such area.....
Good Luck!
Buddy
It Just Doesn't Matter....