I have run alloys through the winter for many years and have not had a problem with pitting. I only keep my cars 4 years maximum though.
When you buy, you should check the online dealers and don't be afraid of Tire Rack in the US as they will quote you a price with the shipping, taxes, duty and brokerages fees included. I have had good experience with them in the past.
Roger Fowler Tires in Kitchener will store your winter tires & wheels (for a fee) for you if they do the swap.
The type of tire you need depends on the car you drive and if you do a lot of out of town driving. A fwd car in Kitchener will work ok, but rear wheel drive is very difficult. Winter tires will be much safer in any case.
Kitchener winters vary considerably, with last year being a bad one.