Well, just in case you didn't notice, above your post there's a bundle with Creeper World 3 available, not sure about how much the bundle and the CW3 cost in canadian dollar but i would say that it's better to buy it from the bundle since you will get the game for the same price + more games.
Unless you want a Steam free version, not sure if the bundle offers that.
I didn't actually see that, but nothing else in the bundle I'd want... (is there anyone that doesn't have SupCom Gold yet?) So if I only wanted CW3 that might be the better deal. But I don't know if I only want CW3 :/
In terms of game, CW3 is the best of the lot, no questions about it. CW1, though, is also very good, but compared to CW3 it feels like a set-back. So if you do get all 3, it will be a disappointment in many ways to play 1 after 3. However, having said that, CW1 is much more 'distilled' in terms of gameplay than 3, and in terms of pure gaming it is very interesting game. The creeper also move much more fluid in 1 than in 3 (I actually prefer the creeper here) where it flowa bit more like syrup. So they are bout very decent games.
The odd one out is CW2. To be honest, it is my least liked game in the series. Turning the view to sideways spoiled it a bit for me, though it have its fans. It does make it a very different game, and well worth trying, as the creeper flow differently and the core mechanics thereby changes.
What happened, though, is that CW1 is the core game, CW2 is experimentation on the theme with many additions and CW3 is going back to the original theme while implementing the additions that worked in CW2 + adding some new ones (flying, mostly) So if you have the chance, and is interested, I would say it is well worth it to get all 3 just to see how a game series can evolve (and they are all three very good games :))