I will start my post by saying "No offenses, Qorax". I am just expressing my views and experience after living in Canada for (almost) 5 years and having lived, visited, and worked in all 3 major job hubs listed above.
Toronto: This is where I live at the moment. Superb city, vibrant, dynamic, fast ~ I am running out of adjectives. This is the biggest with most jobs and most competitors at the same time. It is significantly challenging to get a job break in the field that you belong, reason being tough competition from tons of immigrants like us. I was lucky enough that my employer supported me in moving from Vancouver to Toronto and I was saved from job hunting. Cost of living depends upon your lifestyle but in my experience, it is surely higher than the other two. Fuel, milk, and property purchase are less expensive than Vancouver, apart from that everything is expensive in Toronto. Fuel is cheaper but at the same time car insurance is high, so if you make an annual calculation it either breaks-even or go high. On the positive side, due to Toronto being the first choice to land for most of the immigrants, you will find nice and helpful communities for each ethnicity/race/culture/religion.
Calgary/Edmonton: This is where I worked (commuted every week for 1.5 years). With the slide in oil boom, there is a lot of uncertainty hovering on existing jobs. Needless to say that it significantly impacts the new job postings. Smaller cities, friendlier, more family time, and low cost of living are on the plus side. Weather is definitely on the minus side. Edmonton boasts more government jobs (being provincial capital) and Calgary has more private sector jobs.
Vancouver: This is where I lived for 4 years and my POE to Canada. Green, beautiful, and 'live your life' are few adjectives that click my mind. Usually it is marketed as one of the most diverse cities in the world, but I disagree with that. There are pre-dominantly only three diversities that rule Vancouver. Regarding jobs, very less from industry perspective except tourism and timber. More service class and stable; not as many jobs as Toronto but less competition as well. Cost of buying a property can be super high but at the same time rentals are very less expensive. For most immigrants like me, we look at rent expenditure first. Weather wise it is not as cold as rest of Canada but to live in Vancouver, you will have to love 'rain'. Overall, a fantastic city if you get a descent job. I was lucky enough to get a job that I 'wanted' and I am not denying the fact that Vancouver is the city which gave me whatever I have today in Canada. Again, it does not necessarily mean that the same can be true to others.
On the whole, I would recommend you do your homework about the job/business prospects in your own field in each of the cities. Do not look at the size of the city or natural beauty or even your community preferences. None of these things are going to come to pay your bills and put the food on the table.
All the best.
