To come to Canada and work and then apply for PR is not a very safe option. To me this is too great a risk to take especially if you have kids coming along.
Secure the visa to immigrate to Canada then you come.
Check up the jobs scores in the Canada immigration. Say a welder scores the highest point then go to ITE for a crash course....yea ITE TRADE course...welding, plumbling, car mechanics, laser cutter etc.
Then get some connection to work for FREE doing spare times like Sat or Sun to clock in enough hours of experience. With this trade cert (just entry level is good enough) and with say 1 year of part-tiem experience, you stand a much better chance to get a visa.
I have seem with my own eyes, workers got to leave Canada after their working visa expired.....remember I have lived here for almost 20 years and I sell life insurance .... I meet lots of people and I hear lots of good and bad news.
Henry Ford's famous quote "Whether you think that you can, or that you can't, you are usually right." has its own virtue like positive thinking but then this is beyond positive thinking because there is a immigration law which is beyong positive thinking. His quote does apply good to a NEW IMMIGRATE who uses positive thinking to overcome the odds but not change the law.
Like in Singapore, no matter how positive I am, I have to serve the N.S. and waste my time in the reservist. Of course I can be positive about it as I can enjoy fresh air in the army training and made new friends with the mosquitoes. Beyond that I am screwed.
So please sercure your visa before coming to Canada.
On the other hand, if you come to do a study like technical course or a degree, then you might stand a much better chance to gain employment and later get the visa for P.R.
For the window labourer it might not be classified as labourer but as skilled worker, so he still stand a chance.
But I thought nayr69sg was referring to those Maxican labourers who come to the farms in the summer to work as farm hands....these group of labourers stand almost no chance to get a PR visa.