@cweisg - What you're planning is very different from the rest of the LD community. Most LD riders would never consider doing a IBA ride in a large group. That's one reason why you're not getting much input on large groups crossing the border.
Virtually always when crossing the border with other bikes you will be asked "are you with these other bikes/riders?" You need the first person in your group at the crossing to be very clear and positive that yes, you are with XX people on motorcycles and you're on a group ride. Do
NOT mention the IBA or the SS1K ride, and coach all of your riders to
NOT mention these things, but to just say you're all members of the North Canton Indian motorcycle
group, (not club), and you're enjoying a day ride through Canada, heading for lunch in xxxxx town, then what ever crossing you plan to use. You're in Canada "for the day", not a specific amount of time. Don't mention any time line other than it being a day ride.
I can tell you from first hand experience that if you say you're going to be in Canada for X or XX hours, it triggers a flag and you, possibly your entire group, will be sent to secondary inspection and asked more questions. Border control knows when you entered, when you were last in Canada and will ask you when you were last in Canada when you enter, so tell your people to have some idea when they were last in Canada and be prepared for that question.
When you re-cross the border, just be honest about where you entered Canada and that you're on a day ride,
if asked.
Strictly in my opinion, it would be best if you can honestly say you entered Canada that morning and leave before nightfall. It's going to look suspicious if you enter/exit in the wee hours of the morning or middle of the night. Ditto if you enter in the afternoon/evening and ride through the night. You're only going to be in Canada for ~6 hours. Make those daylight hours. If you've never 'enjoyed' the 401 connector out of Toronto, it sucks. Lots of traffic and erratic drivers.