The Right Retailer
Your local pool store operator is the first expert you might want to contact. After all, you trust him/her for your other pool needs.
Until recently, he/she would likely have drawn your attention to a fuel burning heating system such as natural gas, propane or oil. Given the soaring prices of fuel over the last couple of years, and the likelyhood of fuel costs to hold that trend, he/she will now most likely refer you to an expert in solar heating for swimming pools. If he/she carries a line of solar collectors, insist on being served by a professional who knows more than meets the eye about solar heating. Ask for some specific references, and call these references.
You can also try the Canadian Solar Energy Society of Canada. They can help you find the area representative for the Canadian distributor or manufacturer who will provide company trained and experienced personnel for the installation. Subcontracted installations usually land in the hands of laborers who have installed less than 5 systems, and every installation has it's unique challenges, contrary to fuel burning system installations.
The best rule is: you should buy from somebody you trust, who is courteous, who gives answers to all of your questions with solid evidence, someone who carries a descriptive list of references from which to choose from freely. Your retailler should also show you samples of the major manufacturers as well as a detailed warranty certificate. Purchasing directly from the manufacturer can also have its advantages, with no intermediates to wave the warranty. Who will install the system? If possible, go for the product whose installers are factory trained, and who do this full time, for the supplier.