Being self-employed can be mentioned by you in SOP or in your CV but I think it will harm you just as it will help you. Generally, it may be related to your chosen field of study however it does not fit in the curriculum of a free lancer as one generally pursues education in the hopes of getting a job or moving up in one's career but that doesn't apply in your case as you are already self-employed.
I would suggest that you carefully craft your SOP and CV and follow the notion that you are seeking permanent employment in your own country to dispel any concerns that you are seeking to immigrate to Canada. Try to relate the work experience you had with your experience of job interviews you had in your own country and how a college degree could have made a difference for you.
I think you have a fair chance, however please note that you can only follow one approach if you apply once and then get rejected you can't apply again with a different approach otherwise you will be deemed not credible. It depends on what country you come from so if you have low rejection rates there you should be fine with weak ties.