I've noticed that when I import into LR from canon RAW, the thumbnail that appear upon import (before rendering of previews) looks great and punchy. Very soon after, when the previews are rendered, the image becomes very flat.
Clicking any of the presets in the Develop pane, from Adobe Standard to the ACR's Camera Landscape, don't revert to the initial punchy preview.
So what is LR using to create that initial import preview? How can I get that preset to be my default?
There's nothing applied to my import workflow so there's nothing being done at import.
Also, the camera is set to shoot in Landscape colour mode which I finds suits me best. Does this setting actually affect the raw file? If I shoot in portrait, does the resulting raw differ from if I'd shot in landscape?
The thumbnails shown (and indeed the image shown on your cameras LCD) are jpg images, and therefore have had some minimal processing done to them. Lightroom actually imports the unprocessed RAW file, which is why it shows a little differently to the preview.
It's probably worth setting up a default "Apply during import" profile using settings to your liking, and get LR to use that each time you import
Re: second part bof your question. If you are loading with landscape shoot mode into Lightroom it does not attach those qualities to the raw file.
I shoot Nikon with such picture settings used and the only software which takes account of those settings used and imports / affects the raw file is with NX2 which I use as my main software of choice to this end.