Hi Kelly
I don't think there is any one course which can give you the breadth needed to work competently as a behaviourist. Studying behaviour will give you the tools to 'read' the dog, to know what is genetic or instinct, what is breed specific, what is learned behaviour, and what is affected by the environment the dog is in. A course in psychology will teach you how dogs learn, what effects their ability to learn, how to change and/or modify learned behaviour. But you will also need to know how to train dogs and teach their owners how to train dogs because more often than not by the time an owner comes to you with a problem the dog will not be able to learn/fit in with group training classes. So really, you need to have knowledge and experience in all fields. It helps too if you know a something about nutrition and diet, and neuropsychology. It helps of you can read as many books as you can by reputable authors not those just jumping on the popular 'behaviourist' bandwagon.
After all that, be prepared for a lot of people who nothing about what a behaviourist is, to discredit your knowledge and make fun of what you do not realising how many years of study and application it has taken to get to where you are.
If you can take all that and derive huge satisfaction from turning dogs around you'll have found success.
I wouldn't presume to recommend any particular course but if the course or organisation is accredited to a reputable education body you should do OK.
I wish you well.