I've recently bought the Bell Galaxy s2 LTE HD and am in the same boat as you; it's bloody hard to get info on this phone's battery compatibility. I Even called Samsung Canada, and their battery distributor, microcell, doesn't seem to have replacement options... hopefully some of my initial research can help you. Do not buy the battery for the SGH-I727, as it will not be compatible with your model. All of the non-HD versions of the Galaxy S2 LTE (as well as the Telus Galaxy S2-X) use a four pin battery, while the HD uses a three pin system.
As mentioned in the last post, I'm pretty sure the only thing out there that has a compatible battery is the Galaxy s2 LTE HD SHV-E120L and E120S. I have looked extensively at the images on google, and it appears that this is definitely a three pin battery. I am going to take the plunge and order a package that has 2 OEM batteries and an external charger today (there are some good options and deals on Ebay for this model #, some even claiming up to 2100 mAh), so if you're willing to sit tight to hear whether it works, I can pass on the info when the batteries arrive.
Hope this helps
Update: I just heard from an Ebay seller that she has read that the battery for the Galaxy SII D710 (Samsung Epic 4G Touch) is also compatible. If so, Andida has a battery that is extended capacity, without an increase in size, and I've read some good things about these units. She is going to confirm this with the Andida rep, so I think that's the direction I'll go in if they are compatible (seller is in Quebec too, so delivery would be cheap/fast).