Okay, some further details: after about 24 hours off I've just turned the DVR on, loaded up the guide, and there's my antenna-based channels complete with logos and about 2 days worth of guide content. Interestingly, US HD channels seem to be already mapped as well. If I check out the channel list editor there's a total of 346 off-air and US-cable-based channels in there, about the first 200 with logos so far, but nothing Canadian except for the off-air networks.
Checking the diagnostics screen, the Host Channel is shown as 0:0-17 (off air PBS), but the VBI Host is showing as 0:0-51 - which, if I check it, is an extremely fuzzy PAX. Perhaps I should remove 51 from the DVR's list to prevent any attempt at locking onto such a weak channel?
In the meantime, I've re-enabled Cable in the guide and have again entered my Canadian postal code in an attempt to get Canadian listings. If it doesn't work in a couple days I'll go back to the Buffalo zip code.
From other Sony products sold up here (like the DVD-R/HDD unit) it SEEMS I should be able to get TVGOS...