I would keep the nonstop and waitlist for the later YVR-IAH nonstop.

My decision would be driven above all else by the risk of a cancel/misconnect, both of which seem within the realm of the possible with UAX and/or an ORD connection.

There are worse airports than IAH for that layover. Terminal E UC, shower, grab a bite at Pappadeux . . . .

If you were earning more miles and/or gaining more than 90 minutes in YVR, I might view the choices differently. But don't see enough of a benefit with these two alternatives.