Bullfrogs and Green Frogs are the usual candidates for overwintering as tadpoles if both are in your area. I'm not sure that Leopard frogs usually take more than 1 year to develop, have you seen this happen? I find them hard to ID at this stage.

We had a thaw yesterday and I checked my nearby stream for tadpoles and couldn't find anything moving around yet, but it probably won't be long.