Required by law. Ontario law requires this credential for the work. A contractor without it cannot legally do the job, whatever the quote says. Electricity Act, 1998, O. Reg. 570/05 (Licensing of Electrical Contractors and Master Electricians).
This work usually needs a municipal permit. Unpermitted work has to be disclosed when you sell, and an insurer can decline a claim arising from it.
Ask before you hire
What is your ECRA/ESA licence number?
How old is my roof, and should it be replaced before the panels go on?
What is the payback period using my actual bills, not an average?
Who handles the net metering application with the utility?
What happens to the warranty if you go out of business?
Do not put a twenty-five year system on a roof with eight years left in it.
You asked for the trade Solar and battery, and the words "water heater replacement", and businesses serving Toronto. Of the 12 businesses listed, none match every one of those.
The cost band and the licence requirements above still apply. They are what you need to judge a quote from anywhere else: whether the price is in the range, and whether the person quoting is allowed to do the work at all.
Listings here are seed data for demonstration and are labelled as such on each profile. Cost bands are what GTA homeowners are typically quoted, not offers. Always confirm a licence number against the issuing registry yourself before work starts.