The Australian course is a comprehensive course for those who don't know braille at all...and I found it to be a great refresher for myself (speaking as someone who already knew braille before taking the course). There are two Canadian courses - one for new transcribers and an update certification for those already certified in literary braille. The update course is just that, it looks only at those things that are different. Both courses have positive aspects. You will need to decide if they are worth taking for you. The NLS course for new transcribers is close to being ready...and I know NLS is also working on an update certification for those already certified. I do not know exactly when they will be available...asap is what I hear. 🙂
The next question might be, will agencies accept the Australian or Canada certifications? The answer is, ask the agencies you work for. They are not required to - though I have heard from those I work with that they will accept the Canadian or Australian certifications. Once the NLS certification is available, that may change. Each agency will have to decide that.