i'm not trying to be picky or contrary here, but i am trying to give you honest opinions and to explain why to prevent you from spending a lot of $ and then have it not work out well.
poured concrete strong enough to resist freeze thaw cycles is going to be a heck of a lot more $ than a simple liner in a dug out area. note that the frost depth used in construction for footings is for unexposed depths and not open like what you are talking about having. that's really not something i even have enough experience with to think it a good idea.
i wish i could say otherwise, but blocks above grade for this purpose are just not going to last if you get any kind of freeze thaw expansion of the water up against them.
IMO you'd have to drain the pond to below the blocks at the end of the season to where it is just liner and ground forces to avoid damage. i'm pretty sure you don't want the expense of keeping it heated. i do know that people have bubblers and circulating windmill or solar type things to keep the water moving to prevent it from freezing but if those fail or you get a cold enough snap to freeze then...
i don't really know enough about your winter climate there to wonder if it would work well, but i do hear about snow and cold down that far so i am always leery about what happens when the weather changes. it is so much easier when you have one kind of weather to contend with instead of the changes the seasons bring.
good luck, i do hope it works out.