I flying tomorrow YYZ-ORD-MCI on 2 seperate tickets.

YYZ-ORD on AC, ticketed by AC
ORD-MCI on UA, ticketed by UA

I'm trying to check in online for the UA segment, however it's telling me to check in with an airport agent. Couple of questions:

1) United res is telling me that AC can check me in at YYZ for the ORD-MCI flight. Not sure I buy this, however would UA in Toronto be able to check me in for the United flight?

2) If not, are there check-in kiosks or a customer service desk behind security in ORD where I would be able to check in without having to exit security?

I will not have any bags to check, and have 1 hour 15 minutes in ORD