As you may / may not know, Cantonese is one of the many dialects of the Chinese language, with Mandarin being the 'official' dialect of China. Across almost all of the dialects, the writing and reading part are basically the same. The only catch is that, in mainland China, people write simplified Chinese characters while people in Hong Kong and some part of southern China, write traditional chinese characters. The characters look quite drasticaly different actually.
What is interesting about the Cantonese dialects is that what people speak is actually very different from what they write. So even if you learned written chinese, it is still far from 'learning cantonese'. Even if you are able to speak individual characters in cantonese, the sentence will come out nonsense.
As far as I know, there is no 'grammar' for Cantonese. So don't expect to learn from a formal way. I am sure there will be common short phases tutorial on the internet so you can get a basic conversation going. But at the end of the day, perhaps the most effective way of learning Cantonese is to go and live in Hong Kong.