There are rarely upgrades for cash available at the gate on N American flights. If you want to try and upgrade go to your itinerary online and click on the upgrade button to request an upgrade using e-500 mile coupons. As a general member your upgrade will be eligible to clear 24 hours before each flight..which is behind any upgrader with elite status (ie chances aren't great..but not impossible). If you clear you can purchase the e-500 miles coupons at the airport. They come in blocks of 4 and cost USD$325 per block. It would cost you:

YYZ-ORD-1
ORD-OGG-9
OGG-SFO-5
SFO-YYZ-5

So 20 total... pretty pricey if everything cleared.

You could also use United miles to upgrade (15,000 each way)... or a SWU or CR-1. Any of these instruments are confirmable at booking if there is upgrade space available..otherwise you waitlist.

If you're looking for a trade you will need to post that in the coupon connection.