Well, cover letter is not an essential thing to do, its only when you need to explain any points to visa officer etc. Its simple as you are writing a letter to some one, you can start with Dear Sir/Madam and following your concerns. Hope it helps.
dear sir/madam
please find herewith my file (ur name). i am australian citizen wishing to immegrate to canada under the FSW catagory.
i have a bachelor's degree in science and a 2 years diploma in computer education. since 2007 i am working as a computer trainer for ------ company.
I would like to mention that i m quite good in speaking and writing english.
in view of all the above factors, i believe i m qualified enough to immigerate to canada as a FSW.
thank u very much for ur kind attention and i look forward to hearing from u soon.