i guess that letter of explaination and statement of purpose (SOP) both are same ... in SOP you need to mention the struggle to find the university,
struggle for course ,
why this university ?
why Canada?
your past achievements
and how does this new course beneficial for you ?
what will you do after you are done with this course ? ( in this you need to mention that you will come back to your country and how you will implement your studies here .)
I hope this works out for you .