Jarred (Not canned!) sour cherries are my favorite option. Down here in Louisiana I have never actually seen a fresh sour cherry. Anyway jarred are great, I like to throw in a cup or two of good-quality dried cherries as well. I prefer the Just Cherries, cheap dried cherries will ruin a pie.
My very favorite cherry pie is from Martha Stewart's Baking Handbook. It is the slab pie recipe. Just drain the cherries add in the dried cherries if using, and proceed with the recipe as written. It usually takes 2-3 jars.
That said, I do not have access to frozen sour cherries. I do not know whether they would be better or about the same.
Cherries are a true short-season fruit. Tart cherries are only available fresh for a couple of weeks in July.
Is "canned cherry topping" different than bottled or canned sour/tart cherries in water? I hope so. While the latter cherries lack the perfect texture and color of fresh cherries (as would frozen, btw), they still make good pies. Btw, the cheapest and best bottled sour cherries are often found at Middle Eastern and sometimes Greek grocers (Turkey is famed for its cherries). Trader Joe's also carries them.