VanG, I'm in Michigan with similar season to Toronto. IMHO the contractor corrosion cop-out is largely based on ignorance, especially in a new build where you can select the right materials to avoid potential corrosion.
But as Dave pointed out, SWG requires a tiny bit of consideration due to galvanic process. For example, an inline sacrificial anode is a popular install in my neck of the woods to reduce any possible corrosion, especially on heat exchangers. On retrofits, this is also a consideration for vinyl pools with steel walls.
With low water temps, eg in spring if you open at 50 degrees for exampe, the unit will have difficulty producing chlorine, so you're best to supplement with liquid chlorine on the wedges of shoulder season. There is no other contraindication for swg in terms of climate.
The reality is that swg can be wholly trouble free if one adopts TFP run parameters, and trumps regular chlorination for convenience in my book. But people who think they never have to test, control for ph, sequester metals if on well or occasionally tweak run time -- who expect totally hands off set it and forget it -- are the ones likely to have issues ... But they'd have those issue with any other method too
One last note...the salinity of a SWG is minor compared with, for example, the runoff of salt-treated walkways in winter. But if Toronto has implemented discharge restrictions about SWG, that could influence contractors and would be worth checking. I recently had to change out my water -- all 24,000 gallons -- for a liner change. I'd thought I might kill some grass near my drainage ditch, but its green as can be.
