Well, there's Big Cottonwood, Little Cottonwood, and American Fork canyon/Alpine Loop (quite nice early in the morning). AF to Cascade Springs is my typical Saturday morning ride during the warmer months. It's a worthy climb - for me at least and the scenic beauty rivals just about anywhere.
For steep, LCC fits the bill for most - it's unrelenting 10%-12% grade for about 8 miles. Alpine Loop combined with Suncrest and LCC comprise the bulk of one of the climbing stages of the Tour of Utah. Touted the toughest stage race in the US.
Suncrest on south mountain is not a canyon, but a pretty good climb. I often do the "Double Dip" which is up and over, and then back up and over. The north side is a little tougher than the south side and its rideable right now. You'll have a while before the other options are freed from winter's grip.
I think you'll find any of these options more challenging than Emmigration canyon.