I can’t find any [revenue] fares bookable via UA on AC where you get seats anymore without paying…at least Transborder/domestic Canada flights. Even refundable. Not sure if awards include them anymore - they definitely used to

if you want to book a fare on AC that includes seats, you need to pay for a Flex fare, which in my experience on routes like SFO-YYZ are about $100+ extra over a standard fare. Those flex fares also don’t have a change fee, whereas standard does (If you book via UA, fare rules are UA which means no change fee as long as you aren’t booking basic).

definitely sucks, but welcome to 2025!