I'd skip buying one pre-flashed. Get a stock, unlocked Pixel 9 Pro (Google Store Canada or Best Buy, not a carrier-locked one, or the bootloader may not unlock) and put GrapheneOS on it yourself with the official web installer at grapheneos.org/install/web. It takes about 15 minutes from a Chrome/Chromium browser.
Doing it yourself avoids trusting a reseller's flash job, and you can check the boot key hash afterwards with the Auditor app. Re-lock the bootloader at the end.