I haven't had a ticket to show anyone and no one seems to be interested, even border agents.
From time-to-time I have crossed the US border with two one-way tickets, one outbound, one inbound.
For example, YVR <--> PDX, outbound on AC, inbound on AS, which can't be ticketed as a return trip.
I always have a printout of my confirmation for the return trip, and have produced it when asked. That printout has constituted my 'ticket.'