I hike with my dog all the time and have found that using 1 pole is much better than two. I also have the dog attached to my waist at all times. She's a strong puller and it's way easier to have her attached to my waist than try to hold the leash with my hand.
Here's my set-up:
For day-hikes I have a skijor belt that I use, but for backpacking I added 4mm accessory cord through my hip belt with bowlines at each end. I attach a carabiner through the bowlines and the leash through the carabiner.
I think it's really important, especially if you have a dog that pulls, to have a length of bungee cord as well. My set-up includes a 4 foot section of bungee cord that's attached to another 3 foot section of regular poly rope. That way, when the dog pulls it doesn't jerk either one of us around as much. Do a quick search for skijor lines and you'll see what I'm talking about, and can probably order a line from one of the sites for cheap.
As I said, my dog is a strong puller, so generally the line is taught and we can just walk along comfortably and I use the one trekking pole for support. When she starts sniffing around, is about to get tangled up, or when we are on steep descents I hold the line with my free hand which gives me added support and control. It's been a great system for me and I highly recommend it.
If you do a search on the site I posted a few pictures last winter that show what the set-up looks like. And here is a picture of the set-up in action on the Chilkoot Trail last week:

Edited: To reiterate, having a section of bungee eliminates risk of jerking and throwing you off balance when attached at the waist, even with a dog that pulls hard.