Alright folks, here is the situation. Winter

is coming to Canada, and I need winter tires. I have a "new" 05 Echo and I would like to know, what would be the biggest and/or widest winter and summer tires I could put on this thing without messing with the tech or speedo too much.
And also way off topic, mine is automatic, and I would like to get a tranny cooler for it. I intend to drive this thing until it can't physically driven anymore. And I want it too last. Any ideas on what size or brand etc. I should get?
Any comments, would be great. Thanks!
-Steve