• canoscan 8000f
• I've scanned A4 and A3 (via stitching). Not sure if I've ever encountered the slightly larger 9x12 format, but the scannable area *is* slightly larger than A4, so it might work in this scanner.
• A3 paper you need to stitch (multiple scans). There is automatic stitching software but it isn't always that good at understanding drawings, esp. line drawings. Mostly I throw the scans at Hugin, and if I'm not happy with the result, get each scan as a layer with a layer mask, align them and then put judicious gradients into the mask to combine them. You need to write off a border section of each scan as it will be distorted and shaded as the paper curls out of the scanner bed. I generally go left to right, top to bottom across the paper. It's important to keep the paper in a consistent alignment too (otherwise you'll have to apply rotation or perspective tool pretty precisely).

If you use camera, finding the right distance from the paper is really important (otherwise you'll get lense distortion). Don't fill the entire photo with the drawing -- it should be less (how much less depends on the lens); the picture should also be central.