There is a well known trades shortage, at least to those who have any connection at all to the construction industry. The bottom line is that roughly 50% of the skilled trades are eligible for retirement in the next 5 years and there's no ready supply to pick up the slack. The government, unions, and employers have all finally started to get their act in gear and promote the skilled trades in a way they haven't done for the past 20 years but the uptake still won't meet the demand.
Part of the problem is the perception of the construction industry as the younger generation (and I'm generalizing here) doesn't find slugging it out in all weather and having to travel around as very attractive propositions. It's not the pay because you can easily make $100K+ a year once you've passed your apprenticeship (usually 4 years). There's not to many other jobs out there where you can make that kind of money so quickly without having an advanced university degree. It's the effort required and the negative image that still persists about being a "lowly tradesperson." Remember, the flashy stuff in our world today is technology and high end service industries, not working with your hands and carrying a toolbox to work.
IMO, the only real solution that will be able to fill the demand is to bring in foreigners. There's simply not enough of a home-grown Canadian work force to meet the demand (just because you're looking for work doesn't mean you're willing to work in construction) so we're going to have to start bringing people in, which IMO is a good thing to grow the country (I'd rather bring in skilled trades than refugees).
I know the International Boilermakers Union is already teaming up with employers to bring in foreign welders to meet the demands of the construction industry. Even the government is doing its part (albeit slowly) to reduce the paperwork and bureaucracy that restricts such workers.
The bottom line is that our entire society is going to face a shortage of workers as the baby boomers retire. It will dramatically change the nature of work in Canada as certain types of jobs will either disappear or be restructured to face the simple reality that we don't have enough people to fill the positions we have today. So the next time you see a bag your own groceries line, remember that one effect of this is that we won't need as many cashiers, which is part of the reason grocery stores are trying to find alternative means to getting work done.
p.s., to the comments about union out of work lists being full in certain cities, that's more to do with regional variations and industrial cycles than with the overall picture. Hamilton and Windsor may be in economic downturns but other parts of the province (especially Toronto) are not. By its nature construction is cyclical and part of being a construction worker is saving during the good times so you can weather the bad. If you're willing to move around, you can easily find work in Ontario (or in Alberta or out east). But if you're only willing to work in Hamilton, well yeah, at times you may be sitting on the out of work list for a while.