OLDYELLER, I have the same package as you and before I broke down and got a HD-PVR 8642 (not Nextbox) I did not get the extra HD channels in the Digtal VIP package but yes now with the addition of the HD PVR box I get all the promised channels.
My guide shows my available channels with a grey background and channels I do not get have a black background.
Cant speak for Canadian HD channels but here's a good list of US HD channels and their broadcasting signal formats. What you should notice is that the broadcasting format should be correlated to your STB format. For example if the broadcasting signal is 1080i your STB for that channel should also be set for 1080i or if 720p then your STB should be 720p, etc. to get best picture quality. This is assuming your tv supports HD and various formats up to 1080p.
While that may be true in theory, the Nextbox 3 doesn't let you do it. You have to pick one resolution in the settings and, if necessary, it does a conversion. If you set the NB 3 to 1080i, which is the resolution of most HD channels, it will convert other signals, such as 720p, to 1080i. Conversely, if you set the NB 3 to 720p, it will down convert 1080i. I have an old 8300HD PVR which has a pass-through feature, allowing you to pass through whatever resolution the box is receiving, then the display converts to its native resolution, such as 1080p. The scalers and deinterlacers in displays are usually superior to cable boxes and the like.