Please confirm with USCIS, but there is generally a 180 "grace period" after your US status expiry, meaning these 180 days don't count towards your "unlawful presence", even though you're out of status once your H1B expires.
Also, you can always file a change of status to B1/B2 regardless of your H1B situation, or basically apply for ANY change of status, it can even be NIW green card, anything to keep your status pending as an "authorized stay". USCIS is experiencing huge delays and backlogs now, so it should keep you covered till you get your passports back from Ottawa